Incarnation

The term incarnation was sometimes applied to the bodies/selves/lives of a Time Lord. While it was sometimes used interchangeably with "regeneration", (TV: The Keeper of Traken, Extremis) incarnations were actually the result of this process, with Time Lords regenerating from one incarnation to another.

Barring special circumstances, a Time Lord could only have thirteen incarnations, (TV: The Deadly Assassin) before their symbiotic nuclei started to break down. (AUDIO: Trial of the Valeyard) Some, like the Master (TV: Utopia, AUDIO: Eyes of the Master) and the Doctor, (TV: The Time of the Doctor) have been given new regeneration cycles, bypassing this limit.

Proto-Time Lords created by the Kovarian Chapter had varying numbers of incarnations. (AUDIO: The Lady in the Lake)

Contact between separate incarnations of the same Time Lord constituted a violation of the First Law of Time. (TV: The Three Doctors)

Use of the term
Looking back on their previous lives, the Doctor occasionally used the word incarnation. (TV: The Twin Dilemma, AUDIO: The Light at the End, The Chimes of Midnight, Dead London, Scaredy Cat) He also used it in reference to the Master, (TV: Doctor Who) and others used it to talk about the Doctor's regenerations, as well. (TV: The Ultimate Foe)

The Eleventh Doctor thought he had never used the word incarnation in that capacity but was proven wrong by Ally, from an alternate dimension, who played a clip from Doctor Who of the Sixth Doctor discussing his "last incarnation" in The Twin Dilemma. He conceded but claimed that the word was hardly ever used. (COMIC: The Girl Who Loved Doctor Who)

With the term being sometimes interchanged with the term regeneration, a Time Lord stating they were in their tenth regeneration would be synonymous in saying they were in their eleventh incarnation. (TV: Hell Bent)

When referring to past incarnations, the Doctor would use the plural "mes", faces or lives. (COMIC: Four Doctors) Time Lords might also use the term "bodies" or "body" when referring, generally, to either their own or other Time Lords' different incarnations. (COMIC: Doorway to Hell) On one occasion, the Sixth Doctor used the word "iteration". (AUDIO: The Light at the End)

Time Lords by incarnation
The number of the Doctor's incarnations was complicated; the Eighth Doctor's successor did not use the title of doctor, while the so-called Tenth Doctor once regenerated and kept his face. As such, the Eleventh Doctor had expended all his lives before being enabled to regenerate again by the Time Lords. (TV: The Time of the Doctor) Upon the "birth" of the Thirteenth Doctor, the Doctor had regenerated a total of fourteen times. (COMIC: The Many Lives of Doctor Who) A further incarnation was yet to come. (TV: The Day of the Doctor, COMIC: The Then and the Now)

In her Spacebook profile, identified herself as the ninteenth incarnation of the Master. (PROSE: Girl Power!) It was in this incarnation that she was killed by her predecessor, denying her the opportunity to regenerate. (TV: The Doctor Falls)

Drax was known to have had thirteen incarnations. (AUDIO: The Trouble with Drax)

In his thirteenth and final incarnation, Azmael deliberately regenerated past his limit, killing him and Mestor, who had been attempting to possess Azmael's body after his own was destroyed. (TV: The Twin Dilemma)

As her title suggested, the Twelve was the twelfth incarnation of a Renegade Time Lord who suffered from regenerative dissonance. (AUDIO: Planet of the Ogrons) Other than her, the Time Lord who lasted the longest with this condition shot out both his hearts with a staser in his eighth incarnation. (AUDIO: World of Damnation)

Kenossium was known to have had twelve incarnations. (TV: Hell Bent)

The Doctor
The Time Lords temporarily extracted the Second Doctor, followed by the First Doctor, from their respective time streams to assist the Third Doctor against Omega. The Second Doctor was summoned by Goth while returning to the Land of Fiction to recover his recorder. (PROSE: Future Imperfect) The First Doctor, however, was caught in a time eddy and so could only provide his advice. (TV: The Three Doctors)

After he accidentally awoke an army of Sea Devils who proceeded to attack a submarine in England, the Fourth Doctor unexpectedly came into contact with the Third Doctor, who was accompanied by Jo Grant. Adopting a new identity to protect the timelines, the Doctor helped his predecessor to defeat the Sea Devils, and made a quick exit before the Third Doctor could discover who he was. (COMIC: Under Pressure)

When the Second Doctor's TARDIS became trapped in a pocket dimension that disrupted the link to the TARDIS's interior dimensions and destabilized reality, the High Council gave the Fourth Doctor and Romana permission to go against the Laws of Time and establish a link between the Fourth and Second Doctor's TARDISes so that the Fourth Doctor and Romana could enter the Second Doctor's console room and bring the interior back into sync with the exterior. During this crisis the Second Doctor and his companions entered the console room while the Fourth was still in it, but the future Doctor and Romana hid on the other side of the console from the younger Doctor and his companions and carefully maneuvered around the room to stay out of sight until the Second Doctor left again, at which point they returned to the future version of the ship. (PROSE: Heart of TARDIS)

Lord President Borusa used Time Scoops to bring the first five incarnations of the Doctor, as well as several of their companions, to the Death Zone on Gallifrey as part of his plot to gain Rassilon's gift of immortality. However, the Fourth Doctor and Romana II were caught in a time eddy and so failed to arrive. After Rassilon granted Borusa the gift by confining him in the stone of the Tomb of Rassilon, the Doctors and their companions returned to their respective time and place. (TV: The Five Doctors)

When the Second Doctor was captured by Joinson Dastari and his augmented Androgum associate Chessene, the Time Lords permitted the Sixth Doctor to rescue his past self, allowing him to travel to the space station where the younger Doctor had been captured so that he could trace his abductors. (TV: The Two Doctors)

During Bonjaxx's birthday celebration, the Seventh Doctor and Ace met a future incarnation of the Doctor, who came with his companion Ria. (COMIC: Party Animals)

During his quest to assemble the Key to Time with Ace and Bernice Summerfield, the Seventh Doctor encountered his sixth incarnation while he was fishing with Frobisher. Discussing what difference it would make if they had not left Gallifrey, the Seventh Doctor was unable to convince his previous incarnation of their importance to the cosmos, but acquires his sixth incarnation's cat brooch, a piece of the Key to Time. Following this, the Seventh Doctor went to 1963 to acquire another piece, the TARDIS Instruction Manual. While doing so, he found his first incarnation, whom he tripped up to save him from an Imperial Dalek, which he shoved into the path of an oncoming bus. The Seventh Doctor quickly took his leave, leaving his original incarnation oblivious both to the identity of his saviour and to the danger he was in. (COMIC: Time & Time Again)

According to one account, the Seventh Doctor travelled back to give the Hand of Omega to the First Doctor. (PROSE: Echoes of Future Past)

When the Sirens of Time manipulated the Fifth, Sixth and Seventh Doctors into changing history to give the Sirens more power, the Temperon drew the three Doctors together on Gallifrey after the Sirens had aided the Knights of Velyshaa in their attack on the planet, allowing the three Doctors to learn what had happened and take action to seal the Sirens away forever, apparently erasing these events for everyone but the three Doctors. (AUDIO: The Sirens of Time)

A malfunction in an ancient prototype TARDIS on a human colony drew the Fifth and Seventh Doctors to the planet at different times, with the same disruption preventing the Doctors from simply returning to their TARDISes and leaving until the Machine had been destroyed. During their encounter, the Seventh Doctor began to recall the incident with the Knights of Velyshaa before being cut off by the Fifth Doctor, who had yet to experience that event. The Seventh Doctor also remembered teaming up with his other twelve selves to save Gallifrey. (PROSE: Cold Fusion, AUDIO: Cold Fusion)

The Seventh Doctor met another incarnation who was known as Muldwych. Despite his concerns about the First Law of Time, the Doctor assisted Muldwych in defeating the Charrl. Shortly afterwards, the Seventh Doctor visited Muldwych and had tea with him. (PROSE: Birthright) Muldwych later attended the wedding of Bernice Summerfield and Jason Kane, giving the Seventh Doctor the book The Unformed Heart and two halves of a time ring to use as the wedding rings. (PROSE: Happy Endings)

When the Eighth Doctor lost his memory due to a trap set by the Master, Rassilon gave the Doctor subtle telepathic instructions so that he could still pilot the TARDIS. Under Rassilon's guidance, the Doctor visited all seven of his past selves at key points in their lives so that he could offer them advice and assistance. (PROSE: The Eight Doctors)

The Tenth Doctor accidentally came into contact with the Fifth Doctor when their iterations of the TARDIS colided, resulting in the Fifth Doctor appearing in his successor's' TARDIS control room. This caused a paradox which risked the creation of a black hole that would endanger the universe. However, the Tenth Doctor was able to quickly enact a solution, having remembered watching himself doing so from the perspective of his predecessor. Bidding farewell, the Fifth Doctor returned to his own time soon after. (TV: Time Crash)

At the end of his final reward just prior to his regeneration, the Tenth Doctor collaborated with his immediate successor to save Henry Gordon Jago and George Litefoot from the Gentlemen of the Dice. (AUDIO: The Jago & Litefoot Revival)

When the War Doctor prepared to use the Moment to end the Last Great Time War by destroying the Time Lords and the Daleks on Gallifrey, the sentient weapon brought him as well as the Eleventh Doctor from the Under-Gallery, into contact with the Tenth Doctor in Elizabethan England, where a Zygon incursion had been uncovered. After the three Doctors arranged a ceasefire between the Zygons and humanity in the 21st century, the War Doctor returned to the barn accompanied by his future selves, who had been let through the time lock. When Clara Oswald urged the Doctors to find another way to end the war, they got the idea to transport Gallifrey into a pocket universe on the last day of the Time War. To do so required the work of "all thirteen" of the Doctor's incarnations, up to the Twelfth Doctor. Following this, the Eleventh Doctor returned to the Under-Gallery where, after seeing off his predecessors, made contact with the Curator, an incarnation from his future. (TV: The Day of the Doctor)

Shortly following his regeneration, the Twelfth Doctor made a brief indirect contact with his immediate predecessor when he listened in on a conversation on the phone between Clara and the Eleventh Doctor. The Eleventh Doctor, just prior to completing his regeneration following the Siege of Trenzalore, had made a call to the future to convince Clara to stay with his successor. (TV: Deep Breath)

The Twelfth Doctor recalled to Clara that his first four incarnations had attempted to form a band, only for it to fall apart due to creative differences. (COMIC: Day of the Tune)

Refusing to change despite being mortally wounded by the Cybermen, the Twelfth Doctor was taken by the TARDIS to Antarctica in 1986, where he came into contact with the First Doctor. (TV: The Doctor Falls) The First Doctor, who was nearing his own regeneration, likewise was hesitant to change, and his contact with his successor caused a timeline error which resulted in the appearance of Captain Archibald Hamish Lethbridge-Stewart from World War I, pursued by a glass avatar of the Testimony. After uncovering the nature of the Testimony, as well as changing history so the Captain did not die just prior to the Christmas truce, the two Doctors took their leave of each other, having been convinced to face their respective regenerations. (TV: Twice Upon a Time)

The Thirteenth Doctor visited the Fourth Doctor whilst he was trapped in the pocket dimension controlled by the Scratchman, to give him a reminder of what he stood for and what he had to be in order to encourage him to hold on to his true identity against the Scratchman's power. Once her past self, Sarah and Harry were back on Earth, the Thirteenth Doctor visited the Fourth directly to muse on how important it was that they never give up on being the Doctor. (PROSE: Scratchman)

The Master
When the Master offered to assist the Cult of the Heretic in their plans to remake the universe, they agreed to the offer only if he would kill one of his past selves to prove his loyalty to their cause. As a result, the Master attempted to ambush his past self during his assault on Terserus, but the Cult deliberately sabotaged this attack so that they could create a more potent paradox by transferring the younger Master into the body of his future self and then kill the older Master in his past incarnation. The two Masters were able to escape, but their travels in the wrong bodies nearly destroyed the universe due to the paradox, with whole segments of history being erased- including meetings with the Fifth and Sixth Doctors- until the Seventh Doctor confronted both Masters at once and helped them realize what had happened. The Masters returned to their own bodies and attempted to leave the Doctor to die so that they could hijack the Cult's plan to remake the universe, but the Doctor was able to follow them and restore reality as it was, apart from sending the Masters back to their points of origin with no recollection of their interactions with the Cult (AUDIO: And You Will Obey Me, Vampire of the Mind, The Two Masters).

, the ninteenth incarnation of the Master, (PROSE: Girl Power!) travelled through her time stream to recruit her, Tremas,  Bruce and , forming a band to compete on The Battle of the Bands Beyond the Stars. The group planned to use the popularity of the program to hypnotise the audiences across the galaxy. According to Missy, the five spent "decades" preparing for the performance. (COMIC: The Five Masters) The group went on before the Twelfth Doctor and Clara Oswald due to a shift in the program's schedule, and the five revealed themselves to the pair. (COMIC: The Abominable Showmen) Missy expected the Doctor to attempt to stop the five of them, or to at least esquire on their plans, but the Doctor refused to intervene or question their scheme. After much prying, the Doctor correctly predicted the group's plan, but still refused to intervene as they started their song. As she prepared to hypnotise her audience, her previous incarnations began to fight with her over her device, as each wanted to control the universe without the others. During the fight, viewers began to turn off their sets and the group were soon all disqualified and were thus blown up, although neither Clara nor the Doctor believed that they had truly been killed. (COMIC: The Five Masters)

Missy later inadvertently came into contact with her immediate predecessor aboard a Mondasian colony ship while in the company of the Twelfth Doctor. (TV: World Enough and Time) Though they initially joined forces, Missy ultimately elected to side with the Doctor against the Cybermen, resulting in her being killed without the opportunity to regenerate by her predecessor, though not before she mortally wounded him and thus initiated his regeneration. (TV: The Doctor Falls)

Others
Eleven of Drax's thirteen incarnations teamed up in order to con the Fourth Doctor into stealing a Blinovitch Limitation Effect limiter, which was what allowed them to cooperate on this scheme in the first place. (AUDIO: The Trouble with Drax).