The Doctor

"The Doctor" was the main alias used by a renegade Time Lord from Gallifrey who travelled through time and space with various companions in their obsolete and "borrowed" Type 40 TARDIS. They were the universe's "greatest defender", having saved the cosmos thousands of times throughout a long life, becoming a great legend across the whole universe.

Though largely a believer in non-violent conflict resolution, they were, when absolutely necessary, a great warrior. Indeed, some civilisations in the universe (e.g. the denizens of the Gamma Forests) translated the word doctor as warrior, (TV: A Good Man Goes to War) whilst others saw the Doctor as a compassionate benefactor, worthy of their admiration and compassion. (TV: Last of the Time Lords, The Wedding of River Song) The Doctor said "I serve at the pleasure of the human race", refusing to do anything to significantly alter history unless their human companions told them to. (TV: Thin Ice)

Although they had saved untold numbers on their travels, the Doctor was thought to have caused the deaths of billions at the conclusion to the Last Great Time War. (TV: Dalek) Though most of the Daleks were killed in the crossfire, Gallifrey — disappearing, rather than being burned — was hidden thanks to the efforts of "all thirteen" of their incarnations, the first eleven of which retained no memory of the event. (TV: The Day of the Doctor) For their actions, the Time Lords granted the Doctor a new cycle of regenerations, allowing them to live on after using up all available regenerations in their first cycle. (TV: The Time of the Doctor)

From the latter years of their first incarnation onward, the Doctor had a pronounced affinity for Earth and the human race. After departing Gallifrey, they voluntarily chose to spend time on the planet, (TV: An Unearthly Child, AUDIO: Summer, The Haunting of Thomas Brewster) choosing it as the place of their exile during most of their third incarnation, (TV: Spearhead from Space - The Three Doctors) and even owning property in Kent (COMIC: Fellow Travellers, PROSE: Verdigris, Warlock, Warchild, The Dying Days, Mad Dogs and Englishmen) and New York City. (PROSE: The Forgotten Army) They favoured Great Britain as a frequently visited location, taking most of their companions from there. (TV: An Unearthly Child, Spearhead from Space, The Time Monster, Rose, Smith and Jones, Partners in Crime, etc.) Even before the disappearance of Gallifrey, the Doctor spent much more time on Earth than on their homeworld.

The Doctor's personal history was constantly changing and contradicting itself. (PROSE: Unnatural History)

Name
The Doctor's true name remained unknown to all but a very few individuals, such as Sam Jones, (PROSE: Vanderdeken's Children) River Song, (TV: Forest of the Dead, The Name of the Doctor) and the Master. (TV: World Enough and Time) Though the Time Lords knew the genuine name of the Doctor, (TV: The Time of the Doctor) they did not use it, even in the formal setting of legal trials. (TV: The War Games, The Trial of a Time Lord)

According to, he chose the name "Doctor" to reflect his constant desire to make people "better". (TV: The Sound of Drums) claimed to know the Doctor's real name from their time together on Gallifrey; she said it was "Doctor Who", and the Doctor had chosen it to be mysterious, but dropped the "Who" when he realised it was too on-the-nose. (TV: World Enough and Time)

The Eleventh Doctor told Clara Oswald that his real name was not so important, since he specifically chose in its place the title of "Doctor", "like a promise you make". (TV: The Name of the Doctor) This promise was, as the Tenth and War Doctor recited together, "Never cruel or cowardly. Never give up, never give in." (TV: The Day of the Doctor) The Twelfth Doctor claimed that when he originally adopted the title it was "just a name," which held no real significance until his first visit to Skaro. It was through his opposition to the Daleks that the Doctor was able to define himself and realise who he was. (TV: Into the Dalek)

The title "Doctor" was not undeserved; they did hold one or more doctorates of some sort, (TV: The Armageddon Factor, The God Complex) formally studied medicine on at least 19th century Earth at Glasgow University, (TV: The Moonbase) and frequently displayed detailed medical knowledge. (TV: The Ark, Frontios, The Empty Child, New Earth, The Time of Angels, The Curse of the Black Spot) At least some versions of their sonic screwdriver performed medical scans and healed minor wounds. (TV: The Empty Child, The Vampires of Venice, A Good Man Goes to War) They showed knowledge on how to help someone thrown by an explosion recover quickly. (TV: Remembrance of the Daleks) Although their first, (TV: "The Forest of Fear", "Mighty Kublai Khan") fourth (TV: The Ark in Space) and fifth incarnations (AUDIO: Red Dawn) had claimed not to be a doctor of medicine, their third, (TV: Spearhead from Space) ninth (COMIC: The Cruel Sea) and tenth incarnations (TV: Utopia) claimed to be a doctor of practically "everything", and by their eleventh life, the Doctor claimed to hold doctorates in at least medicine and cheesemaking. (TV: The God Complex)

According to Evelina, the Doctor's name was written in the stars of the Medusa Cascade. (TV: The Fires of Pompeii) Members of an unidentified race of pan-dimensional beings also knew the Time Lord's real name, at one point. (AUDIO: The Last Voyage)

In one account, he had taken the moniker after his first contact with humans. Colonists on the medical/penal colony of Iwa began calling him "Doctor" after his arrival. He failed to correct them. After they left the planet, "the Doctor" simply kept the name he had been given by the humans. (PROSE: Frayed) In another, he had already been introducing himself by that name after his first trip in the TARDIS, which gave an alternative account of meeting humans for the first time on the Moon. (AUDIO: The Beginning) He responded to the name when an echo of Clara Oswald put it to him before even departing Gallifrey. (TV: The Name of the Doctor)

River Song believed that the Doctor had influenced the etymology of the noun doctor, and was, in several languages, the original source of the word. (TV: A Good Man Goes to War)

According to Dorium Maldovar and the Silence, the oldest and most dangerous question in the universe was "Doctor who?" The Doctor's true name was apparently the answer. Dorium claimed the Doctor had been running from the question all his life. According to the Silence, "silence must fall when the question is asked," (TV: The Wedding of River Song) because if the question was answered, it could lead to destruction on a universal scale, through several methods, each of which were located on the planet Trenzalore. The first was that the Doctor's name could be used to open his grave and alter his timeline, potentially undoing the countless times the Doctor had saved the universe. (TV: The Name of the Doctor) The second was that his name could be used to confirm to the Time Lords, who were sealed in a pocket universe and had been broadcasting the question throughout the entirety of time and space, that it was safe for them to return; which could result in another Time War. (TV: The Time of the Doctor)

At some point River Song learned his name, prompting the Doctor to claim that there was only one reason he ever would or could reveal it. (TV: Forest of the Dead) Indeed, even while spending hundreds of years in a town permeated by a Truth Field and hearing the question asked multiple times, the Doctor would not or could not answer. (TV: The Time of the Doctor) However, River later stated that she "made him" tell her his true name and that it "took a while". (TV: The Name of the Doctor)

Clara Oswald viewed the Doctor's name in a book on the Time War, contained in the TARDIS library. She subsequently lost the information when time was rewound. (TV: Journey to the Centre of the TARDIS)

The Seventh Doctor mentioned to Trevor Sigma that his nickname at college was Theta Sigma. (TV: The Happiness Patrol) His classmate Drax called him by this nickname. (TV: The Armageddon Factor)

Moments before regenerating into the Thirteenth Doctor, the Twelfth Doctor used his last words to leave his future self some advice. Amongst these last words was that the future Doctor must not tell anyone their name, but that they couldn't understand it even if the Doctor did tell them. The Doctor went on to state that "children can hear it, sometimes. If their hearts are in the right place and the stars are too. Children can hear your name. But nobody else, nobody else ever." (TV: Twice Upon a Time)

Age
The Doctor's age was a matter of great confusion, as they provided many inconsistent statements. The Second Doctor once gave his age in Earth terms as 450. (TV: The Tomb of the Cybermen) On two separate occasions, the Third Doctor implied that he may have been several thousand years old. (TV: Doctor Who and the Silurians, The Mind of Evil) The Fourth Doctor, however, gave his age as "something like 750 years". (TV: Pyramids of Mars) Immediately after his sixth regeneration, his seventh self claimed to be 953. (TV: Time and the Rani) The incarnation that fought in the Time War considered himself 400 years younger than the Eleventh Doctor, who was purportedly 1200 at that time. (TV: The Day of the Doctor) The Tenth Doctor claimed to be 903. (TV: Voyage of the Damned) Also, at least prior to leaving Amy and Rory behind, (TV: The God Complex) the Eleventh Doctor maintained an age less than his seventh incarnation. (TV: Flesh and Stone, The Impossible Astronaut)

The Eleventh Doctor later claimed to the Ponds that he was 1200 years old (TV: A Town Called Mercy) but clarified to Clara Oswald that he'd lived so long he'd forgotten whether or not he was lying about his age. (TV: The Day of the Doctor) The Twelfth Doctor, after spending 900 years defending Trenzalore, stated his age to be over 2,000. (TV: Deep Breath)

The Twelfth Doctor spent approximately four and a half billion years (TV: Hell Bent) trapped inside his confession dial in an energy loop. In each loop, the Doctor would die, providing energy to a teleporter which would "print" another copy of himself as he was when he first arrived. Although this kept his body from ageing, he claimed to remember the living through every single version of the loop. (TV: Heaven Sent) He later stated to that he was in fact four billion years old. (COMIC: Doorway to Hell)

Romana I once caught the Fourth Doctor "rounding down" his age, (TV: The Ribos Operation) while the Eighth Doctor once flatly admitted that he didn't necessarily use the same definition of the word year each time he gave his age to someone, usually changing his age depending where he was in the universe. (AUDIO: Orbis)

The Eleventh Doctor once told Solomon that he was probably a Sagittarius. (TV: Dinosaurs on a Spaceship)

Before the Time War
The Doctor's familial relations were unclear at best. According to one account, the Doctor was one of the forty-five cousins created by the Loom of the House of Lungbarrow on Gallifrey. (PROSE: Lungbarrow) However, the Doctor also stated several times that he was born to a human mother. (TV: Doctor Who, PROSE: Alien Bodies, The Infinity Doctors, Grimm Reality, Unnatural History, The Shadows of Avalon)

The Tenth Doctor told Sally Sparrow that he was "rubbish at weddings, especially [his] own". (TV: Blink) An earlier incarnation had also been wed, (PROSE: Cold Fusion) to Patience and they were said to have had a number of children, and grandchildren. (PROSE: The Infinity Doctors) The Doctor had, in the Tenth Doctor's own words, been "a dad" (TV: Fear Her) and "a father". (TV: The Doctor's Daughter) These children were "sons or daughters, or both." (PROSE: The Eleventh Tiger) The Twelfth Doctor claimed he had "[d]ad skills." (TV: Listen) Clara Oswald also claimed the Doctor had "children". (TV: Death in Heaven)

According to Clara Oswald, as well as children, the Doctor also had "grandchildren". (TV: Death in Heaven) These included Susan Foreman, (TV: An Unearthly Child) John and Gillian. (COMIC: The Klepton Parasites) Some accounts referred to Susan as "the Other's" granddaughter but recognised the Doctor as him. (PROSE: Lungbarrow)

The Doctor had at least one brother, Irving Braxiatel, who became an associate of the Doctor's onetime companion, Bernice Summerfield. (PROSE: Tears of the Oracle) Braxiatel was also a cardinal on Gallifrey (AUDIO: Weapon of Choice) and was the owner of the Braxiatel Collection, (PROSE: Tears of the Oracle) which the Doctor and Romana once compared to the Louvre in Paris. (TV: City of Death) The Doctor had one niece by Irving Braxiatel, Maggie Matsumoto. (AUDIO: The Empire State)

At one point, the Doctor became the adoptive father of a female Time Lord named Miranda Dawkins, whom their eighth incarnation reared until her mid-teens. (PROSE: Father Time) Miranda later gave birth to a daughter, Zezanne, and died while trying to protect the Doctor. (PROSE: Sometime Never...) The Man with the Rosette attended the Doctor's wedding to Scarlette, sitting at the table reserved for the Doctor's family. (PROSE: The Adventuress of Henrietta Street)

The Doctor also had a great-grandson named Alex, the son of Susan and David Campbell. (AUDIO: An Earthly Child) Alex went on several adventures with the Eighth Doctor and backpacked around the Earth with Lucie Miller, before they were both killed by the Daleks. (AUDIO: Lucie Miller, To the Death) Susan and David also had adopted children, Barbara, Ian and David Junior (PROSE: Legacy of the Daleks) — meaning that the Doctor was an adoptive great-grandfather as well as a biological one.

Before the Last Great Time War, some of the Doctor's family had died or gone missing. (TV: The Tomb of the Cybermen, The Curse of Fenric, AUDIO: To the Death) After the last day of the Time War, the Tenth Doctor, while telling Donna that he'd been a father before, explained that he "[l]ost all that a long time ago along with everything else." (TV: The Doctor's Daughter)

Even after Gallifrey and the Time Lords were revealed to have been saved from their fate at the end of the Time War and sent to a pocket dimension by all thirteen Doctors, the Twelfth Doctor still apparently believed his missing children and grandchildren to be dead, as Clara Oswald, masquerading as the Doctor, stated as such to the Cybermen. (TV: Death in Heaven)

After the Time War
Genetic material from the Doctor in their tenth incarnation was used to create a daughter, Jenny. The Doctor explained to Donna Noble and Martha Jones that due to the way his DNA was processed, he was Jenny's "biological mother and father". Although initially spurning her, he soon considered Jenny his daughter and invited her to travel with him in the TARDIS. Before she could join him, however, she was shot. The Doctor believed Jenny to have died, and departed. Unbeknownst to him, she survived, and set out on her own life of adventure. (TV: The Doctor's Daughter)

When the Earth was relocated to the Medusa Cascade, a clone of the Doctor was created; this clone later was exiled by the Doctor to an alternate universe. Technically, the clone could be considered a relative of the Doctor's. Also, Sarah Jane Smith referred to the Doctor's companions as his family, saying, "You act like such a lonely man, but you've got the biggest family on Earth!" (TV: Journey's End)

Affairs
The First Doctor was accidentally engaged to Cameca in the 15th century. (TV: The Aztecs)

After Gallifrey was destroyed in the War, the Eighth Doctor married Scarlette in order to ceremonially tie himself to the planet Earth. (PROSE: The Adventuress of Henrietta Street)

The Tenth Doctor romanced and later married Elizabeth I. (TV: The End of Time, The Day of the Doctor, PROSE: Suspicious Minds) She later declared him an enemy after he failed to return as promised. (TV: The Shakespeare Code) The Tenth Doctor implied he had been married several times prior to Queen Elizabeth, as he remarked to Sally Sparrow about being "rubbish at weddings, especially [his] own". (TV: Blink) In his eleventh incarnation, the Doctor accidentally became engaged to Marilyn Monroe, and married her the same night in what he later claimed was not a real chapel. (TV: A Christmas Carol)

River Song often hinted that she and the Doctor had a physical relationship somewhere in her past and his future relative to the Eleventh Doctor's encounter with the Silence in Florida. (TV: Silence in the Library /Forest of the Dead, The Time of Angels /Flesh and Stone, The Pandorica Opens /The Big Bang, Day of the Moon) The Eleventh Doctor, operating a Teselecta shaped like himself, performed a "quick version" of a wedding ceremony with River because they were in the middle of a combat zone in an alternate reality. They repeatedly referred to each other as husband and wife after the ceremony. (WC: Asylum of the Daleks Prequel, TV: The Wedding of River Song, The Angels Take Manhattan, The Name of the Doctor, The Time of the Doctor, AUDIO: The Boundless Sea, Five Twenty-Nine, The Eye of the Storm, PROSE: Suspicious Minds)

According to Clara Oswald, by the time of the Doctor's twelfth incarnation, the Doctor had been "married four times, all deceased". (TV: Death in Heaven)

Languages
The Ninth Doctor said he could speak five billion languages. (TV: The Parting of the Ways) The Doctor's native language was probably Modern Gallifreyan, but they seemed to prefer speaking English, (TV: The Mind Robber) always with an accent that was similar to accents used in the British Isles. (TV: An Unearthly Child, The Power of the Daleks, Spearhead from Space, Robot, Castrovalva) This accent changed from incarnation to incarnation. For example, both the Seventh (TV: Time and the Rani) and the Twelfth Doctor (TV: The Time of the Doctor) spoke with an accent similar to one used in Scotland. Both Rose Tyler and Harriet Jones noted the accent of his ninth self sounded like he came from "the north" or was "a northern accent", referring to the north of England, with the Doctor once retorting that "lots of planets have a north". (TV: Rose) American Grace Holloway once told a San Franciscan policeman that the Eighth Doctor was "British". (TV: Doctor Who)

They could read and write Old High Gallifreyan, (TV: The Time of Angels) a skill unusual even among Time Lords. (TV: The Five Doctors) He spoke the language of the Judoon, (TV: The Stolen Earth) Delphon (a language "spoken" using only eyebrow movements), (TV: Spearhead from Space) several Chinese languages, (TV: The Mind of Evil, The Talons of Weng-Chiang) Ancient North Martian, (TV: The Waters of Mars), venusian (TV: The Curse of Peladon) and Tritovore (TV: Planet of the Dead). They knew at least some Sycoraxic (TV: The Christmas Invasion) and a language of Tiaanamat, which sounded like canine barking to human ears. (TV: The Rings of Akhaten) He did not seem to understand French in his second incarnation, (TV: The War Games) but later became fluent in it across several periods of French history. (TV: The Girl in the Fireplace) They also claimed to have spoke "sabre-toothed tiger" (PROSE: Sick Building), "baby" (TV: A Good Man Goes to War, Closing Time), "cat" (TV: The Lodger), "horse" (TV: A Town Called Mercy), and "dinosaur". (TV: Deep Breath) By their eleventh incarnation, the Doctor purportedly "spoke everything". (TV: A Good Man Goes to War, Closing Time) They once understood British Sign Language; by their twelfth incarnation, though, the Doctor had lost the skill, saying that it had been "deleted" from his languages and replaced with semaphore instead. (TV: Under the Lake)

Influence
The Doctor belonged to the Prydonian Chapter, the most important chapter of Time Lord society. (TV: The Deadly Assassin) They had a profound influence on many worlds and was written into their histories; (TV: Forest of the Dead) as a result, the Doctor was the recipient of many honours, including being made a noble of Draconia (TV: Frontier in Space) and a knight (and enemy) of the British Empire. (TV: Tooth and Claw) An incarnation of the Doctor once pulled Excalibur from the stone. In their twelfth incarnation, the Doctor told Clara Oswald that he became "King of England for a day" before abdicating in order to give King Arthur the throne. (PROSE: Silhouette)

Having broken the Time Lords' non-interference policy, in their second incarnation he was put on trial as a renegade. (TV: The War Games) Subsequently, for a time, he acted as an agent of the Time Lords' Celestial Intervention Agency before the beginning of his sentence on 20th century Earth. (PROSE: Players, World Game) Following his defeat of Omega, which saved Gallifrey, he was granted a pardon and given his freedom. (TV: The Three Doctors)

In their fourth incarnation, as part of a ploy to outwit invaders of Gallifrey, the Doctor was a candidate for the position of Lord President of the Supreme Council. (TV: The Invasion of Time) In their fifth incarnation, he was put on trial again for recklessness. (COMIC: The Stockbridge Horror) He was later given the title of Lord President by Councillor Flavia, against his wishes. He pretended to accept the office but ran away in his TARDIS. (TV: The Five Doctors) Prior to the Doctor's trial during their sixth incarnation, he was deposed in absentia and put on trial for breaking the non-interference policy and later in the same trial, for genocide. The validity of the trial was called into question when it was discovered it had been orchestrated by an evil future manifestation of the Doctor, the Valeyard, and mooted. (TV: The Trial of a Time Lord) As the War Doctor he also fell out of favour with the Time Lords during the Last Great Time War. However, due to the Doctor's efforts to save Gallifrey and the Time Lords, they seemed to forgive his actions. (TV: The Day of the Doctor) During the Siege of Trenzalore, when the Eleventh Doctor was on the verge of his final death, the Time Lords responded to Clara Oswald's plea to help him, a plea in which she stated that after all he'd done he'd earned their help and if they loved him, which they should, then to help. In this instance, the Time Lords saved the Doctor by giving him a new regeneration cycle (TV: The Time of the Doctor) rather than letting him die permanently as had happened in an alternate timeline. (TV: The Name of the Doctor) After returning to Gallifrey by means of his confession dial, the Twelfth Doctor stood against Lord President Rassilon who tried to execute him. However, the Gallifreyan military hailed him as the man who ended the Time War and also respected him for his reputation during the Time War as someone who didn't need to go into battle armed to win and sided with him. Rassilion's own firing squad, the General and a squadron of military ships backed the Doctor against Rassilon who was overthrown and exiled from Gallifrey along with the High Council. The Doctor used his new position as Lord President of Gallifrey to save Clara Oswald's life before once more fleeing Gallifrey in a stolen TARDIS, a fugitive once more. (TV: Hell Bent)

The Doctor's influence on the universe was seen most notably while in River Song's World: desperate to save the Doctor from his impending death, River Song built a timey-wimey distress beacon telling all of time and space that the Eleventh Doctor was dying and needed their help, causing the entire universe to reply that they would help. River told the Doctor that his impact on the universe was so profound that if he ever needed its help, he just had to ask. This was also shown in how the crew of the Teselecta, though formerly enemies of the Doctor, were willing to aid him in any way they could and kept his secret of being alive from the rest of the universe despite their past, just because he asked them to. (TV: The Wedding of River Song) By the time the Vashta Nerada took over the Library, the Doctor was so well known he was in the Library's books and whatever they read there scared the Vashta Nerada (who the Tenth Doctor didn't think could be stopped) enough that they agreed to his demands. River Song also stated that she believed that "all the skies of all the worlds might just turn dark" if the Doctor ever gave up on helping people. (TV: Forest of the Dead) Nardole told the Twelfth Doctor that, if he died, "everybody in the universe might just go cold". (TV: Twice Upon a Time)

When the Great Intelligence changed time so that the Doctor's victories were negated, Madame Vastra said that the universe was going to be a much darker place without him and entire star systems were shown disappearing as a result of his victories being negated. (TV: The Name of the Doctor) When the Time Beetle created a parallel world around Donna Noble where the Doctor never met Donna, the Earth at least was shown to be a much darker place without the Doctor there to defend it. When the apparently unstoppable Darkness started approaching, Rose Tyler was sure the only one who could stop it was the Doctor, stating that they needed him "more than ever" to stop this reality-threatening event, although she later realised that both the Doctor and Donna together were needed. (TV: Turn Left) During the Last Great Time War, when the Eighth Doctor died during a spaceship crash, the Sisterhood of Karn resurrected him and offered to help him control his regeneration precisely because they believed only the Doctor could stop a war that threatened the existence of the entire universe. Ohila told the Doctor specifically that he was the universe's last hope and indicated that if he took on a more active role in the Time War, which he had avoided doing up to that point, it could be stopped without everything being destroyed. (TV: The Night of the Doctor)

Perhaps the Doctor's greatest influence was on their companions, who were inspired by the Time Lord to fight injustice and help those in need. (TV: Death of the Doctor) Even those who hadn't ever met the Doctor were inspired by his exploits (TV: Planet of the Dead, The Power of Three, The Day of the Doctor, etc) even though he never considered himself to be a hero. (TV: The God Complex, Robot of Sherwood, Death in Heaven)

While talking with the First Doctor, a glass avatar of Bill Potts learned that he had originally started travelling in hopes of finding an answer to how despite overwhelming odds, good always triumphs over evil in the universe. Bill suggested that it was "some bloke", "wandering around, putting everything right when it goes wrong". The First Doctor expressed doubt over this theory, not realising that Bill was referring to the Doctor himself. Bill understood that the Doctor could not see his own impact on the universe, on everyone who ever met him though she knew everyone else could see it. The Twelfth Doctor told his predecessor that "our lives are woven throughout time and space," and the two of them trying to die twice in the same lifetime was enough to cause an error in the timeline. (TV: Twice Upon a Time) ""The universe generally fails to be a fairy tale. But that's where we come in.""

- The Twelfth Doctor to the First Doctor

Biographical summary
The Doctor had a variety of different origins; most often, they had always been a Time Lord from Gallifrey, but sometimes they had always been a human-Gallifreyan hybrid or a human from the 49th century. (PROSE: Unnatural History) Sometimes, the Doctor believed they had been woven from a loom, and sometimes they believed there had been a mother and father. (PROSE: The Scarlet Empress)

While in bed inside a barn and crying over not wishing to join the army, a young First Doctor heard Clara Oswald assuring him that it was all just a dream, that it was OK to be afraid of the dark and that "if you're very wise and very strong, fear doesn't have to make you cruel or cowardly". (TV: Listen) This was an ontological paradox from when the Doctor's tenth incarnation told Clara about the promise he made about the Doctor being "never cruel or cowardly", which the Doctor had originally heard from Clara as a child. (TV: The Day of the Doctor)

The Doctor left Gallifrey and became a hero who fought evil and injustice across the universe in violation of the Time Lords' non-interference policy. (TV: The War Games) Technically, he explored only with the intention of experiencing the wonders of the universe and having fun, but frequently became embroiled in machinations and crises that ended with him defeating the foe and saving the planet he was visiting. He travelled with many companions, beginning with his granddaughter, Susan Foreman, who also came from Gallifrey. (TV: "An Unearthly Child", "A Desperate Venture", Gridlock) The Twelfth Doctor once stated to a broken Dalek that it was his first encounter with the Daleks on Skaro which truly defined his character. (TV: Into the Dalek) According to Robin Hood after learning of his history from Clara Oswald, the Doctor was a man born into wealth and privilege who couldn't stand the plight of the weak and oppressed and so was eventually inspired to steal a TARDIS and fly amongst the stars, protecting those who couldn't protect themselves. However, the Doctor refused to see himself as a hero. (TV: Robot of Sherwood) He later declared that he wasn't a good man, a bad man, an officer, a hero or a President as he was described by the many who had come to know him over the years, but simply an idiot, in a box, who travels around helping and learning. (TV: Death in Heaven)

Eventually, he was called to account for his crimes against the Time Lords during his second incarnation, when he called them to stop the War Lord and return kidnapped humans to their own era. His punishment was a forced regeneration, exile to Earth in the 20th century, and the loss of his knowledge of how to control the TARDIS. (TV: The War Games) This knowledge was restored to him after he helped to defeat Omega. (TV: The Three Doctors)

Afterwards, he resumed having adventures with many companions in their following incarnations. Early in their fourth incarnation he was sent by the Time Lords to prevent the creation of the Daleks, but despite having the chance he refrained from committing genocide. (TV: Genesis of the Daleks) After this he kept the Black Guardian from obtaining the Key to Time, (TV: The Armageddon Factor) achieved the office of Lord President of Gallifrey, (TV: The Invasion of Time, The Five Doctors) and was again put on trial in his sixth incarnation for breaking the non-interference policy. He discovered that the Prosecutor, the Valeyard, was a personification of his future evil self, who was helping to cover up the crimes of the High Council of Time Lords. (TV: The Trial of a Time Lord)

During the Last Great Time War between the Time Lords and the Daleks, the Eighth Doctor refused to be a part of it. He died in a spaceship crash on Karn, but was revived by the Sisterhood of Karn, and agreed to regenerate into a warrior. (TV: The Night of the Doctor) The Doctor then fought in the War. (TV: Dalek) He ultimately ended the war, and was able to save Gallifrey with the help of his other twelve incarnations. This displacement of Gallifrey caused the near-extinction of the Daleks. (TV: The Day of the Doctor) The War was sealed in a time lock, making it impossible to time travel to it to save Gallifrey. (TV: The Stolen Earth)
 * For details on the Last Great Time War and its survivors, see the separate article.

In an alternate timeline, the Doctor's grave was on Trenzalore, where he had died after a battle. The Doctor was buried in his TARDIS. Instead of a body, the TARDIS contained the Doctor's time stream, manifesting as a column of light. The Great Intelligence forced the Eleventh Doctor to go to Trenzalore to open the TARDIS, though it was opened by a data ghost of River Song. The Great Intelligence entered the timestream to alter the Doctor's history, but the Doctor was saved by Clara Oswald scattering herself through his timestream. Due to this Clara had helped the Doctor many times through his lives, even telling the First Doctor which TARDIS to steal. (TV: The Name of the Doctor)

After believing for four hundred years that he had destroyed his own people, the Doctor finally learned the truth when the Moment united his warrior, tenth and eleventh incarnations in an effort to change the Warrior's mind about destroying the Time Lords to save the universe. This encounter gave the Doctor a new perspective on his Warrior incarnation, stating both that the Warrior was the Doctor more than anybody and that the Warrior was the Doctor "on the day it was impossible to get it right". However, both the Warrior and the Tenth Doctor retained no memory of this encounter and both continued to believe that they had destroyed Gallifrey and the Time Lords when in reality all of the Doctor's incarnations had come together to save it. (TV: The Day of the Doctor)

Eventually the time came for the Doctor to go to Trenzalore where he was fated to die in battle. The Doctor spent centuries protecting the town of Christmas from various enemies including the Daleks, Cybermen, Sontarans and the Weeping Angels as the Time Lords were trying to return to the universe through a crack in time there. Growing extremely old and frail, the Doctor came to the end of his life as he no longer possessed the ability to regenerate. By that point, the Doctor had given up completely, having long before forsaken any chance to flee the planet and save his own life and believing he was unable to change his own future due to the Time Lords being gone. His companion, Clara, refused to give up and pleaded with the Time Lords through the crack to help the Doctor, stating that after all he'd done for the universe, he deserved their help. As the Daleks prepared to kill the Doctor, who was dying of old age by that point anyway, the Time Lords intervened to save him: they granted him a new cycle of regenerations through the crack. This allowed him to destroy the Dalek force attacking the planet and change the future. He later regenerated into the Twelfth Doctor but lost the chance to bring back the Time Lords as even though the enemies assaulting Trenzalore were defeated, the Time Lords closed the crack after helping him. (TV: The Time of the Doctor)

The Doctor's incarnations
By regenerating, the Doctor's personality and outer form changed greatly over time, though all of their incarnations were essentially the same person, retaining the memories, curiosity, eccentricity, and wisdom of the ones before.

The Doctor was known to have regenerated on at least fourteen occasions. The Doctor's first thirteen incarnations were male; (TV: The Day of the Doctor) their thirteenth self broke this mold. (TV: Twice Upon a Time)


 * The First Doctor was an unreadable, guarded figure who was, at first, slow to trust newcomers who learnt of him, but once his trust had been earned, he would show another side of himself as a staunch anti-authoritarian with a mischievous streak. This Doctor was often irascible. He made his anger obvious. He was protective of the young women he took on as companions; they reminded him of his granddaughter, Susan. This Doctor was a brilliant, often short-tempered scientist and keen strategist. He used his signet ring to help get himself through ordeals due to his physical age impeding him. He stole a TARDIS and took his granddaughter with him, joyriding through all space and time, without a clue as to how to drive the thing.
 * The Second Doctor, in contrast, was warm and wise. He was as surprised and frightened of alien menaces as those who faced them with him. He had a knack for manipulation and deception, and especially enjoyed to play a buffoon in order to trick his opponents into underestimating him so that he could better carry out his plans. His predecessor would refer to him as a "clown" due to his bumbling nature. He loved tootling on his recorder and carried around a 500-year diary, trying to record his travels, but ended up discarding it. He wore a big fur coat that dwarfed him, tying it closed with twine. A "cosmic hobo," he was forever getting himself in and out of trouble.
 * The Third Doctor was a more dashing figure than his predecessors. He was described by his first incarnation as a "dandy". (TV: The Three Doctors) He had a penchant for inventing gadgets and was skilled at martial arts, particularly Venusian aikido, and owned a vintage car named Bessie. His initially contentious relationship with Brigadier Lethbridge-Stewart softened into a close friendship during his exile on Earth, lasting through his future regenerations, despite not always agreeing with his actions. (TV: Doctor Who and the Silurians) He also displayed great affection for his female companions, particularly Jo Grant. He was a gallant action hero who was very protective of his companions.
 * The Fourth Doctor was more eccentric than his previous incarnations. Rarely without his long scarf, he carried jelly babies in his pockets, using them as bluffs, gifts and distractions—and occasionally snacks. He relied on his considerable charm, luck, and experience to get through bad situations. Although he retained his fondness for Earth (TV: The Stones of Blood), he ended his regular association with UNIT almost immediately upon his regeneration and only occasionally returned to the planet. However, he had not properly resigned from the position. (TV: Pyramids of Mars) He hated to work and preferred travelling (TV: Robot) but liked history. He enjoyed the company of a wide range of individuals, such as Sarah Jane Smith, aide to his previous self, (TV: Robot) Leela, a savage, (TV: The Face of Evil) K9, a robot dog, (TV: The Invisible Enemy) and even a fellow Time Lord in Romana. (TV: The Ribos Operation)
 * The Fifth Doctor was fond of cricket and wore a stick of celery on his lapel. After a difficult regeneration, this Doctor displayed energy, compassion and innocence not seen in his predecessors. His character was very human and vulnerable. Like them, he used improvisation as the best way out of a tricky situation. The Fifth Doctor was the first incarnation since the First Doctor to go "hands free" and forgo the usage of a sonic screwdriver after having it destroyed. He occasionally wore glasses, even though he didn't need them; he only wore them to make himself look clever. (TV: Time Crash) He was the first Doctor to sacrifice himself for another, when he and Peri Brown were dying from Spectrox toxaemia; with only one dose of the antidote available, he gave her the cure rather than taking it himself.
 * The Sixth Doctor was a grandiose and eloquent incarnation. He sported a multi-coloured wardrobe that was often commented and sneered at, occasionally leading to him being mistaken for a jester. This Doctor loved a good quote, often making one he deemed appropriate during an adventure. He also proved to have great acting skills on numerous occasions. (TV: Mindwarp, The Ultimate Foe) His manic personality and acerbic wit could shade into moral passion, but his lack of concern for little things disgusted his companions. He was also capable of violent action, much more so than his past lives, and of killing without remorse when his life was threatened. (TV: The Two Doctors) Despite his bluster he still could show great compassion and empathy. Like the Fourth Doctor, he spent most of his travels with a single companion.
 * The Seventh Doctor had a voice touched by a Scottish burr. A keen strategist and scientist and especially early in his life, lighthearted, this Doctor was a planner of the highest order. Embracing the complexities of time travel and his ability to manipulate and plan for the future, the Seventh fully embraced his role of Time Lord, even if it risked alienating his companions. (TV: The Curse of Fenric) However, he wished to help heal psychological scars from which his companions suffered. (TV: The Greatest Show in the Galaxy, Ghost Light)
 * The Eighth Doctor showed a romantic and sensitive side not displayed by previous Doctors. Less morally flexible than his immediate predecessor, the Eighth Doctor suffered from bouts of amnesia, first after his regeneration and again after Gallifrey was destroyed following the War with the Enemy. (PROSE: The Ancestor Cell) He broke down after the death of his Great-Grandson Alex Campbell and companion Lucie Miller, who died defeating a Dalek invasion of Earth. (AUDIO: To the Death) Unlike other Doctors, the Eighth spent his travels crossing between parallel universes (AUDIO: Zagreus, PROSE: Time Zero) and amidst time paradoxes, making his personal timeline hard to piece together. (PROSE: Interference - Book One, Interference - Book Two, AUDIO: Storm Warning)
 * The "War Doctor" was an incarnation specifically chosen to be that of a warrior who would fight in the Last Great Time War. The regeneration into this incarnation was aided by the Sisterhood of Karn. (TV: The Night of the Doctor) Although being a warrior and showing anger if he was referred by his former name, he still showed charm and compassion like his earlier selves. Due to the belief that he had destroyed Gallifrey, he was treated with shame and contempt by his future incarnations. His eleventh incarnation stated that his actions broke "the promise" of the "name of the Doctor". (TV: The Name of the Doctor) This assessment changed somewhat once the real end of the Time War was revealed and was described after that as being the Doctor most of all by his future selves. (TV: The Day of the Doctor)
 * The Ninth Doctor considered himself the sole Time Lord survivor of the Time War (he spent his life thinking that he was responsible for destroying the Time Lords). He displayed much of the playfulness of his previous incarnations, but was emotionally and psychologically scarred by the war and his role in it, which sometimes resulted in a detachment that was interpreted by some as cruelty. (TV: The End of the World, Dalek) When asked about his voice and accent, he responded, "Lots of planets have a North." (TV: Rose) He cared deeply for Rose; he began to heal thanks to her. (TV: Dalek) He also made dry jokes when facing danger or to diffuse tension. The Ninth Doctor ultimately sacrificed himself to save Rose's life, not only proving his affection for her, but allowing him to make peace with his past. (TV: The Parting of the Ways)
 * The Tenth Doctor had a manic personality with a fondness for human pop culture references. However, his more outgoing personality traits largely existed to hide leftover emotional trauma from the Time War. While he had a bright, playful side, darker traits occasionally emerged. (TV: The Christmas Invasion, Tooth and Claw, School Reunion, The Runaway Bride) He continued his previous incarnation's love for Rose Tyler, though he was unable or unwilling to express his exact feelings. (TV: Doomsday; Journey's End) He experienced other romances on occasion, including with historic figures Madame de Pompadour (TV: The Girl in the Fireplace) and Queen Elizabeth I. (TV: The End of Time, The Day of the Doctor) However, they all ended badly. He was also the first Doctor to explicitly fear and dodge regeneration, because he had grown attached to his attributes and felt like it was a form of death and loss of identity; indeed, he is the first Doctor to actually undergo a regeneration (after being shot by a Dalek) yet retain his appearance and personality (TV: Journey's End, The Time of the Doctor). When the time came for him to fully regenerate, he was completely heartbroken before accepting his destiny. (TV: The End of Time)
 * The Eleventh Doctor exhibited a renewed youthful enthusiasm for adventure. He could quickly turn frantically angry and ruthless when events demanded. (TV: The Eleventh Hour, The Beast Below, A Town Called Mercy) Like his Second and Seventh selves before him, he was a cunning schemer, executing temporally complex plans and misdirections to achieve victory against his enemies. (TV: Day of the Moon, A Good Man Goes to War, The Wedding of River Song) He frequently referred to himself as being old, showing his age on more than a few occasions. (TV: Vincent and the Doctor, The Big Bang, The Impossible Astronaut, Closing Time) Through his marriage to River Song, he found a sense of family again with her and his in-laws, and was distraught when circumstances separated him from them. (TV: The Power of Three, The Angels Take Manhattan, The Name of the Doctor) Some events still provided painful reminders of his role in the Time War. (TV: The Rings of Akhaten, The Time of the Doctor, et al.) He was the final incarnation before the Time Lords granted him a new regeneration cycle.
 * The Twelfth Doctor displayed an acerbic wit coupled with sarcasm. Like his seventh incarnation, he was manipulative and practical to a fault. He lacked much of the empathy present in his immediate predecessors, and as a result found himself coming off as callous or uncaring on many occasions. In spite of this he shared the Eleventh Doctor's lack of tact and odd behaviour. He had a tendency to brush off death around him, in order to focus on the task at hand. However, because of this he expressed doubt as to whether he was a "good" man. (TV: Into the Dalek) He eventually accepted that he wasn't a good man, but decided he wasn't a bad one either, being just "an idiot with a box". He was also not completely uncaring as shown when Clara Oswald tried to force him to help her save Danny Pink and he stated afterwards that even though she betrayed him in the worst way, it didn't change his willingness to help her or how much he cared. (TV: Dark Water, Death in Heaven) This incarnation had the same face as Lobus Caecilius, a man whose family he once saved from the eruption of Pompeii (TV: The Fires of Pompeii); the Doctor did not remember this until following the (initial) death of Ashildr he had an epiphany about his purpose (TV: The Girl Who Died). Although less affectionate than his predecessor, at one point dismissing his eleventh incarnation's infatuation with Clara as "a mistake", the Doctor and Clara's relationship, especially after the death of Danny Pink, deepened to the point where his infatuation increased into an obsession with her safety and fear of losing her, leading him to threaten all of space and time on a 4.5-billion-year gambit to undo her subsequent death; although he successfully rendered her functionally (if temporarily) immortal, he was forced to erase most of his substantial memories of her. (TV: Face the Raven; Heaven Sent; Hell Bent) This incarnation subsequently used the hard-earned lesson of the loss of Clara to finally resolve his relationship with River Song, allowing her to finally meet her own fate after having put it off since his eleventh incarnation. (TV: The Husbands of River Song) At the end of his life, the Doctor expressed a similar desire not to change as the Tenth Doctor, going so far as to actively resist regeneration. After a final adventure with the First Doctor and having his memories of Clara restored by a glass avatar of Bill Potts, the Doctor chose to regenerate and continue protecting the universe, stating that one more lifetime wouldn't kill anyone except him. (TV: The Doctor Falls, Twice Upon a Time)
 * The Thirteenth Doctor was delighted, upon regeneration, to find out that she was a woman. She found her new form "brilliant", and gave a warm smile at the sight of her reflection. (TV: Twice Upon a Time)

A number of other incarnations have been chronicled; however, where they fall within the Doctor's lifetime is unclear:


 * The Watcher was a manifestation of the Doctor during his fourth regeneration. He went back in time to the Fourth Doctor's final adventure and ensured the events leading to his death would still happen. When the Doctor finally regenerated, he merged with the Watcher to briefly become him, after which he emerged from the regeneration as the Fifth Doctor. (TV: Logopolis)
 * The Valeyard was, according to the Master, an amalgamation of the darker sides of the Doctor's nature, somewhere between the Doctor's twelfth and final incarnation. He shared the characteristics and dress sense of the Master. He sought to take the Sixth Doctor's seven remaining regenerations and have them for himself. (TV: The Ultimate Foe) He was finally defeated in Victorian era London. (PROSE: Matrix) The Great Intelligence (TV: The Name of the Doctor) and the Testimony were aware of the Valeyard's existence. (TV: Twice Upon a Time)
 * Dokien was an incarnation of the Doctor that was good friends with Irving Braxiatel. (PROSE: The Collection) This Doctor travelled to an alternate world and taught King Arthur. He became known as Merlin. (PROSE: Battlefield, TV: Battlefield)
 * Muldwych was an incarnation of the Doctor that lost his TARDIS and was exiled to Antýkhon. He resembled a rotund old man and often wore a red cloak. He was often visited by the Seventh Doctor. (PROSE: Birthright) He eventually escaped Antýkhon through puterspace. (PROSE: Happy Endings)
 * Supposedly, the Doctor's last incarnation both faked his death on Dronid during the first battle of the War and eventually actually died, with his corpse being planted there and becoming the Relic. (PROSE: Alien Bodies)
 * The Curator was a future incarnation of the Doctor. (COMIC: The Then and the Now) He greatly resembled an older version of the Fourth Doctor. His eleventh self wanted to eventually retire and become a curator. (TV: The Day of the Doctor)

An interesting aspect of the Doctor's personality was that they occasionally expressed a personal liking or disliking for particular incarnations, though this opinion depended on the incarnation making the assessment. The Doctor's tenth incarnation expressed a deep fondness for his fifth incarnation, and slight disdain for his ninth, considering him unnecessarily violent. (TV: Time Crash, Journey's End) The Twelfth Doctor was obviously flattered when he believed, incorrectly, that his companion was romantically involved with a fellow teacher he considered to bear a resemblance to his eleventh incarnation. (TV: The Caretaker) The Fifth Doctor was disliked by his immediate successor. (TV: The Twin Dilemma) In another instance, the Fourth Doctor made reference to the Third Doctor, saying, "Some people liked it, but I prefer this one." (TV: The Brain of Morbius) The Twelfth Doctor told his first incarnation that "there [were] a few false starts [before becoming him], but you get there in the end". (TV: Twice Upon a Time) The Seventh Doctor was also annoyed when he had to work with the Fifth Doctor, seeing him as "not even one of the good ones". The Fifth Doctor was equally disgusted by what he would become. (PROSE: Cold Fusion) The Fifth Doctor also stated after meeting his past selves that he was not the man he had been - and "thank goodness for that!". (TV: The Five Doctors) Immediately before his regeneration, the Tenth Doctor stated, "I don't want to go", showing he had become attached to his current self. Immediately after his twelfth regeneration, the Eleventh Doctor remarked upon his new nose, stating that, "I've had worse" — possibly a reference to multiple incarnations, including his third, who was once described as a "long-shanked fellow with a mighty nose". (TV: The End of Time, The Time Warrior) The Eleventh Doctor also at one point expressed loathing for his first incarnation's initial personality, considering himself at that time a foolish and arrogant liar and a selfish coward. (COMIC: Hunters of the Burning Stone) Before learning the true outcome of the Time War, the Eleventh Doctor expressed an even greater hate for the "War Doctor" whose actions were so shameful that he went against "the name of the Doctor" and not counting him among his incarnations. (TV: The Name of the Doctor) Both the Tenth and Eleventh Doctors however forgave their war incarnation and honoured him as being the Doctor more than any of his incarnations once they learnt the real result of the Time War. (TV: The Day of the Doctor)

Adventures by unknown incarnations of the Doctor
Due to the Doctor's many adventures it was sometimes unclear as to which incarnation of the Doctor experienced them. Some of these adventures include:
 * A Doctor was working on behalf of the Time Lords. He was described as having a harshly, angular face and thumb-tucked arrogance. (PROSE: From Eternity)
 * An incarnation of the Doctor after his sixth one visited Peri Brown on Krontep. (PROSE: Reunion)
 * A Doctor once saved a young girl from a monster living in her barn. This incarnation bears similarity to the Sixth Doctor. (PROSE: The Colour of Monsters)
 * A Doctor was once trapped on a Dalek-occupied planet. (PROSE: The Dalek Factor) He used the name Professor suggesting the Seventh Doctor or later. (TV: Dragonfire et al.)
 * A Doctor once met Vastra, Jenny and Strax at the Tower of London in 1897. (COMIC: The Giant's Heart)

Impacting future incarnations
The Doctor on occasion performed acts that are expected to have an impact on future incarnations. Once, in order to recharge the TARDIS, the Tenth Doctor transferred some of his life energy, an act he acknowledged shortened his life-span (and, by extension, the life of his ultimate final incarnation) by ten years. (TV: Rise of the Cybermen) Later, the Twelfth Doctor gave up some of his regeneration energy to revive Davros (TV: The Witch's Familiar); when River Song did something similar to save the Eleventh Doctor's life, it was stated that doing so cost her ability to regenerate (TV: Let's Kill Hitler), so the long-term impact of the Twelfth Doctor's sacrifice remains to be seen. The Twelfth Doctor, after being rendered blind, once created a device capable of borrowing eyesight from a future version of his current incarnation, but at the possible cost of being permanently blinded or future regenerations disabled; however, as this is took place in a computer-generated simulation, it is unclear whether it's possible for the Doctor to create such a device in the real world. (TV: Extremis)

Regeneration
Due to the unique structure of Time Lord biology, the Doctor had the ability to regenerate, to "cheat death". (TV: The Parting of the Ways) A Time Lord was usually limited to twelve regenerations. (TV: The Deadly Assassin, Mawdryn Undead, Doctor Who, The Time of the Doctor) The High Council of the Time Lords could influence regenerations, treating them as punishment (TV: The War Games) and reward. (TV: The Five Doctors, Utopia, The Time of the Doctor) At times, enemies coveted the Doctor's future regenerations and tried to take them for their own. (TV: Mawdryn Undead, Doctor Who, Human Nature/The Family of Blood, The Witch's Familiar)

The effect of regeneration on the Doctor in the time immediately following the event varied from incarnation to incarnation. In some cases the Doctor regained their faculties quickly, erratic behaviour notwithstanding. (TV: The Power of the Daleks, The Twin Dilemma, The Eleventh Hour) On one occasion when the regenerative process was postponed for a long time, he was rendered amnesiac. (TV: Doctor Who) In most cases the Doctor was incapacitated for a period of time before ultimately recovering. (TV: Spearhead from Space, Robot, Castrovalva, Time and the Rani, The Christmas Invasion) There were also rare cases where the Doctor was able to delay regeneration from setting in for an extended period of time. The Tenth Doctor once did such to visit all of his past companions - though, after the long delay, the resulting energy release was catastrophic for the TARDIS. (TV: The End of Time, Death of the Doctor) After gaining a new regenerative cycle, the Twelfth Doctor did something similar while trying to decide whether or not to regenerate. The Twelfth Doctor would call this period "a state of grace" where he is briefly restored to health before weakening, and must either regenerate or die. Like the Tenth Doctor, the Twelfth Doctor's regeneration was highly explosive as a result. (TV: Twice Upon a Time) In contrast, the First Doctor's regeneration into the Second Doctor, despite having delayed his regeneration like the Tenth and Twelfth Doctors, was not explosive at all. (TV: The Tenth Planet) However, the Twelfth Doctor did delay the change further after the First Doctor left, (TV: Twice Upon a Time) and the Tenth Doctor delayed it longer than the Twelfth, having managed to visit every single one of his previous companions before changing. (TV: Death of the Doctor)

Due to the regeneration into the War Doctor and the Tenth Doctor's aborted regeneration, the Eleventh Doctor was actually the Doctor's last incarnation until the Time Lords gifted him with a new regenerative cycle at the end of that life. (TV: The Time of the Doctor) It was unclear exactly how many regenerations he was given, the Twelfth Doctor stated that he himself was not sure and didn't rule out the possibility that his new cycle could be infinite as he stated he could now possibly regenerate forever. (TV: Kill the Moon) Indeed, Rassilon, while threatening the Twelfth Doctor with his gauntlet, remarked to him "how many regenerations did we grant you? I've got all night." (TV: Hell Bent)

Causes of regeneration

 * The First Doctor was weakened by Mondas as it drained Earth's energy, succumbing to old age. (TV: The Tenth Planet) He hesitated for a time to regenerate, fearing the change, entering "a state of grace" where he was briefly restored to health before he had to make a choice. Following an adventure with the Twelfth Doctor, the First Doctor chose to regenerate after seeing the man he would ultimately become. (TV: Twice Upon a Time)
 * The Second Doctor had regeneration forced upon him by the Time Lords as part of his punishment for breaking the Laws of Time; his appearance was chosen for him after he rejected all choices. (TV: The War Games)
 * The Third Doctor suffered radiation poisoning from the Great One's web of Metebelis crystals, then got lost in the Time Vortex for a decade before returning to UNIT HQ. (TV: Planet of the Spiders, PROSE: Love and War)
 * The Fourth Doctor was severely injured after plummeting from the Pharos Project radio telescope. (TV: Logopolis)
 * The Fifth Doctor suffered exposure to unrefined Spectrox, sacrificing himself to give the bat's milk needed to cure it to Peri. (TV: The Caves of Androzani)
 * The Sixth Doctor was compelled to travel to the Lakertyan System by a mental impulse sent to him by an alternative future Sixth Doctor, in order to stop the Valeyard from stealing the lives of every Time Lord to ever exist. Upon arrival, his TARDIS was bombarded by radiation coming from Lakertya, radiation that was deadly to Time Lords. He died from exposure to said radiation. (AUDIO: The Brink of Death)
 * The Seventh Doctor was lightly injured after being caught in the middle of a gang war; his circulatory system was damaged by Grace Holloway during surgery to "fix" his abnormal heart-beat. (TV: Doctor Who)
 * The Eighth Doctor regenerated after he tried to help a pilot named Cass escape from a crashing ship. Cass refused his help however, when she identified his ship as a TARDIS and therefore his being a Time Lord, who she despised because of the Time War. He died when the ship crashed, but was revived temporarily by the Sisterhood of Karn, who not only offered to trigger his regeneration, they also offered him a choice on the characteristics of his next incarnation. (TV: The Night of the Doctor)
 * The "War Doctor" regenerated because his long-lived elderly body had grown precariously weak after spending an entire lifetime fighting in the Time War. The tipping point was at the end of the war, when he helped to save Gallifrey from being destroyed by one billion-billion Daleks and place it in a different dimension. With the Time War concluded and his will to persist as that incarnation for as long it waged settled, his regeneration began before his vitality drained entirely. He remarked that his body was "wearing a bit thin," like his distant predecessor. (TV: The Day of the Doctor)
 * The Ninth Doctor removed the Time Vortex's energy from Rose Tyler, channeling it back into the heart of the TARDIS. However, his brief possession of the energy very nearly destroyed his cellular structure completely. Because of the damage, he had to regenerate. (TV: The Parting of the Ways)
 * The Tenth Doctor was grazed by a shot fired from a Dalek's gunstick during their 2009 invasion of Earth. He used his regeneration energy to heal himself, but then siphoned off the rest of the cycle into his extra hand to prevent his full transformation into another form. The regeneration energy stored in the hand allowed it to grow into another Doctor, when it came into contact with Donna Noble. (TV: The Stolen Earth/Journey's End)
 * The Tenth Doctor absorbed the radiation from a nuclear vault supply to spare Wilfred Mott. Unlike most of his predecessors, he held off the regeneration for a long time; the result was explosive damage to the TARDIS when he finally completed the process, that caused it to crash and regenerate itself. (TV: The End of Time)
 * The Eleventh Doctor spent centuries defending the town of Christmas, on the planet Trenzalore. Before his body succumbed to old age, he was granted a new regeneration cycle by the now-surviving Time Lords and began the process when standing on top of the Clock Tower on Trenzalore. This was perhaps his most destructive regeneration process yet, as he destroyed several Daleks and their ship with the regeneration energy. It restored his body to a younger form, but did not immediately change him into his next incarnation. The change finally occurred shortly after he returned to the TARDIS. (TV: The Time of the Doctor)
 * The Twelfth Doctor fought against the Cybermen on a 400 mile long colony ship reversing from a black hole, causing time to move at different speeds. Following the death and conversion of his companion, Bill Potts, the Doctor was confronted by two versions of the Master. While escaping the bottom of the ship, he was electrocuted and later started to regenerate, though he held it back. After being struck several times by Cyberman energy beams during the Battle of Floor 0507, the Doctor began to regenerate again until he detonated the entire floor. (TV: The Doctor Falls) Upon awakening in the TARDIS, the Doctor again started to regenerate, but held it back, entering "a state of grace" during which he went on a final adventure with the First Doctor. After the adventure, the Twelfth Doctor chose to regenerate after some parting advice to his future self. The Twelfth Doctor regenerated explosively, severely damaging the TARDIS like his regeneration into the Eleventh Doctor had done. (TV: Twice Upon a Time)

"Doctor Who"
The use of the name "Doctor Who" when referring to the Doctor is commonplace in the British media, the end credits of many episodes, and most prose and comic stories of the 1960s and 1970s. The ending credits for the series gave his name as "Doctor Who" or "Dr. Who", from 1963 until Logopolis part four, when incoming Doctor Peter Davison insisted upon a change in the credits of Castrovalva to "the Doctor", which remained in place until the end of the original series in 1989; executive producer Russell T Davies used "Doctor Who" when the series returned in 2005, but Tenth Doctor actor David Tennant asked to change it back to "the Doctor" beginning with The Christmas Invasion. Despite these insistences, both Davison and Tennant called the character "Dr. Who" in several different interviews, as is common for media and cast members.

Especially in the 1960s and early 1970s, many stories referred to the Doctor as "Doctor Who". The Doctor Who annuals and Target Books novelisations frequently called him "Doctor Who" in titles and narration, though dialogue between characters usually used "the Doctor". In The War Machines, WOTAN directly referred to the Doctor as "Doctor Who", but most other usages of the name throughout the series' history were non-serious, such as the Second Doctor's pseudonyms and K9's jokes. In World Enough and Time, told Bill Potts that the Doctor originally called himself "Doctor Who"; the Twelfth Doctor told Bill that Missy was trying to wind her up, but never denied the claim.

Casting
, every actor to portray the Doctor on an ongoing basis has been Caucasian, and born in the United Kingdom. Every actor until Jodie Whittaker had been male. Despite the fact that the Doctor is not a native of Britain, or of Earth for that matter, every actor to play him so far has had a British accent, much in the way most aliens in the Star Trek franchise tend to speak with an American accent. The type of British accent has varied from one incarnation to the next. The earliest incarnations used RP, whereas some of the more recent incarnations have had Estuary accents. The Ninth Doctor had a Northern accent, causing Rose to ask why an alien would have a Northern accent, to which he replied, "Lots of planets have a north." (TV: Rose) Both Sylvester McCoy and Peter Capaldi used their natural Scottish accents while playing the role, with the fact the Doctor sounds Scottish being used in dialogue plot points in (to date) TV: Deep Breath and Robot of Sherwood. The Thirteenth Doctor has a Yorkshire accent. (TV: Twice Upon a Time)

To date the oldest actor to be cast as the Doctor has been John Hurt, who was 73; the youngest has been Matt Smith, who was 26 when cast. The oldest to be cast on an ongoing basis was Peter Capaldi, who was 55 when he was cast and began filming, and turned 56 during production of Series 8. In 2014, Tom Baker turned 80 and continued to record new performances as the Doctor for Big Finish Productions' Fourth Doctor Adventures audio dramas, making him the oldest actor to play the part in an officially licensed capacity. Peter Davison, Colin Baker, Sylvester McCoy and Paul McGann, all in their fifties, sixties or seventies, also continue to portray the Doctor in licensed audio dramas produced by Big Finish, with McGann also appearing in audio dramas produced by Big Finish and BBC Radio for broadcast on BBC7 radio. In the 2000s and 2010s, Tom Baker also portrayed the Doctor in AudioGO's Hornets' Nest, Demon Quest and Serpent Crest audio dramas.

In the Sarah Jane Adventures episode Death of the Doctor Part 1, Daniel Anthony, who plays Clyde Langer, became the first non-Caucasian actor to play the Doctor, when Clyde's body is briefly taken over by the Eleventh Doctor's consciousness. Anthony delivered a line of dialogue as the Doctor while impersonating Matt Smith's voice. Owing to the brevity of the performance, and the fact he is playing an established incarnation, the fact Anthony was the first to break the barrier of skin colour is generally not recognised. Aged 22 at the time the episode was filmed, Anthony is also technically the youngest to play the part.

Although the character is portrayed as white, there have been black actors who were considered for the role. Among them comedian Eddie Murphy back in 1996, David Harewood, Charles Venn, Paterson Joseph and Robbie Gee. Colin Salmon was a strong contender to play the Eleventh Doctor.

Longest-serving Doctor
There are several different methods for calculating who was the "longest serving Doctor". The most commonsensical definition is simply that of the actor who played the role on television for the longest continuous period. This mantle goes to Tom Baker, who was the Fourth Doctor from June 1974 to March 1981, or 6 years, 9 months. Baker is also the longest-serving Doctor in terms of number of individual episodes, total story count and amount of screen time. Thus he is generally considered to be the "longest-serving Doctor".

But there are other methods of measurement — all of which exclude Dimensions in Time.
 * For 92 of the 104 Saturdays that comprised 1964 and 1965, William Hartnell's credit appeared after each episode of Doctor Who without fail. He did sometimes take a holiday and pre-film the odd insert, but, to paraphrase WOTAN, "Dr. Who was required" for all but six weeks in both 1964 and 1965. Call Hartnell the "longest-serving-within-a-single-year-Doctor". Troughton is the closest Doctor to this record, but by 1966, Doctor Who was getting more like an eight- or nine-week gap each year.
 * Peter Davison holds the record for the greatest length of time between his initial performance in the last episode of Logopolis, and Time Crash. The two events were separated by 26 years 8 months. Though he is not playing the same incarnation of the Doctor, Tom Baker's appearance as the Curator in The Day of the Doctor as a possible future version of the Doctor could mean his tenure in the role was longer than Davison's by this measure, with the gap between the 50th Anniversary special's broadcast and Baker's first appearance being just 8 months short of 40 years.
 * Colin Baker had the longest run between bookending regeneration scenes. The span from the premiere of The Twin Dilemma to his regeneration in The Last Adventure was approximately 31 years.
 * Paul McGann was notionally the longest-serving incumbent in the role, as he debuted in May 1996 and Christopher Eccleston's premiere didn't happen until March 2005. Being very generous, therefore, McGann was the "current Doctor" for a total of 8 years and 10 months. However, this is probably stretching a point, since obviously he was actually replaced not once but twice by the BBC. He effectively lost his incumbency once Richard E Grant was cast as the Shalka Doctor.
 * McGann also has recorded by far the greatest amount of hours of Doctor Who audio stories. Previously, he had more performed material on audio and television combined than even Tom Baker, but in 2010, Baker began recording audio dramas for AudioGO and then Big Finish, and had reclaimed his title by 2015.
 * The Eighth Doctor, though not McGann himself, is the longest-serving incumbent comic strip Doctor, in terms of the amount of time between his debut in Dreadnought on 1 June 1996, and his final appearance in The Flood on 2 March 2005. Call it 8 years and 9 months.
 * The Tenth Doctor is the longest-serving comic strip Doctor, in terms of the total number of stories which featured his incarnation. This is primarily due to the number of different publications that were granted comic licences during David Tennant's tenure in the role. Most of this count is due to the prolific comic strip published in Doctor Who Adventures which, for most of Tennant's tenure, was a weekly publication that ran a new standalone story every issue.
 * The situation with books is a very close battle between the Seventh and Eighth Doctors, both of whom had long-running series. However, the Eighth Doctor is the longest-running both in terms of time and number of books published, as seen at this list of novels per Doctor.

The issue of the longest-serving Doctor was a source of controversy on British game show, which asked the question with the choices of McCoy, McGann, Eccleston, and Tennant; the team split their £650,000 between McCoy and McGann, only to find out that the "correct" answer was Tennant. Once the error was discovered (partly since the question was fundamentally flawed due to the absence of Tom Baker), the team was brought back to continue where they left off with £325,000 and ended up winning £25,000.

Analogous characters
There have been several characters outside the confines of the DWU which have been broadly modelled on general aspects of the Doctor. Such "pastiches" are examined in greater detail elsewhere.

The Doctor's wives
Steven Moffat, in his production notes column in DWM 482, speculated that the Doctor's first spouse out of the four mentioned in the television story Death in Heaven was a woman who was married to the First Doctor for a long time on Gallifrey and bore the Doctor's children. He claimed "Mrs Who No 1" was never mentioned by the Doctor nor has he ever discussed her.