Sixth Doctor

Bumptious, melodramatic, and above all stubborn, the Sixth Doctor instantly believed himself superior to almost anyone he encountered. He would often browbeat others into submission with his savage wit and his grammarian's interest in language. Even so, his mercurial and flippant tendencies did not define the true heart of his persona. Beneath his thunderous and turbulent exterior, he was quite the opposite: a passionate, warm, virtuous and empathetic individual.

He was profoundly difficult with his first companion, Peri Brown, whom he initially challenged for her use of American English and her as-yet-incomplete education. Indeed, during the early hours after his regeneration he physically assaulted her due to post-regenerative paranoia. It took considerable time for himself and Peri to stop bickering and speak together on amiable terms, but the Sixth Doctor eventually became someone she could rely upon. With enough distance from the regenerative event, she was able to look to the Doctor for strength after her mother's death.

Despite his bluster, the Sixth Doctor did possess great reserves of compassion. His gentler side began to blossom largely as a consequence of travelling with Evelyn Smythe, a university lecturer whose verbal dexterity was on a par with his own. Also helpful to this transition were Frobisher, a shapeshifting private eye who often masqueraded as a penguin, Flip Jackson, a young woman from twenty-first century London, and Melanie Bush, a brilliant computer programmer from Earth in the 1980s.

A dominant feature of his life was yet another Time Lord trial. Though this one sought to blame him for a shifting docket of crimes, it in fact turned out to be an elaborate ruse. He later found himself in a reverse situation where he became the prosecutor against the Valeyard, the malicious being that had framed him in an attempt to steal his regenerations. He discovered that the Valeyard's dubious existence was somehow tied to his own and took shape from his inherently darker characteristics.

Long after this trial, the Doctor was slowly manipulated by the Valeyard across different moments of his life until the Valeyard had the means to replace all Time Lords in existence. Forced to arrange his own demise to prevent this genocidal plot, the Sixth Doctor was influenced by his next incarnation into inadvertently crossing paths with, who dealt him a fatal blow. He regenerated, putting his future in the hands of his successor.

Alternate timelines
In an alternate timeline, the Doctor became President of the Time Lords, and, in his sixth incarnation, led a battle in the war with the Daleks. With the assistance of the Master, the Daleks began winning the war. Rather than letting them take control of the universe, the Doctor activated the Armageddon Sapphire, destroying the entire universe. (PROSE: The Quantum Archangel)

In one alternate timeline, the Doctor had his throat slit by Shockeye. In another, he saved Oscar Botcherby's life by arriving thirty seconds before Oscar was killed by Shockeye, instead of thirty seconds afterwards. (PROSE: So Vile a Sin)

In a negated timeline, the Doctor and Peri were forced to land in a pocket universe by travelling to 23 November, 1963, where had summoned the first eight incarnations of the Doctor to set off a conceptual bomb inside the mind of Bob Dovie, so that a thought that he would think would become reality. When Dovie entered the Fifth Doctor's TARDIS, his refusal to accept its existence caused the TARDIS to explode in its own timeline until it never existed. Encountering the Seventh Doctor and Ace, and after being contacted by CIA agent Straxus, the Sixth Doctor discovered that the Master had blackmailed the CIA into giving him the weapon. The Sixth Doctor then expanded the dimensional stabiliser on Straxus' TARDIS and was able to summon his other seven incarnations to help stop the Master. The Fifth Doctor went further back in time to 1962, and showed Dovie the TARDIS then, so that he would not be dumbfounded by the TARDIS's interior and therefore preventing the bomb's detonation. The First Doctor completed the restoration by turning off the automatic distress actions, which were what brought all the Doctors together in the first place, so that none of the events had ever happened. (AUDIO: The Light at the End)

When the Eighth Doctor arrived at the Sixth Doctor's trial, the Valeyard was able to force an alternate timeline where a guilty verdict was delivered against the Sixth Doctor on genocide charges. Rescued from execution by his eighth incarnation, the alternate Sixth Doctor created by the Valeyard's actions accompanied him to Gallifrey. The two set up a Presidential Inquiry into their current trial. The Sixth Doctor managing to deliver his own testimony before the timeline that created him ceased, leaving the Eighth Doctor to continue the investigation into the trial, to the point of bringing in Borusa to stabilise the situation. (PROSE: The Eight Doctors)

When the Cybermen allied with Rassilon to take over history, the Doctor found that the Cybermen had taken over the Matrix during his battle with the Valeyard. (COMIC: Prologue: the Sixth Doctor)

In a timeline where a Dalek invasion of Earth in 1903 was thwarted by the Doctor and Evelyn, the British Government trapped the Doctor in the Tower of London along with the two surviving Daleks to keep him as a symbol of their victory, cutting off his legs in order to keep him trapped. Driven insane over the years, the Doctor sometimes spoke to hallucinations of Evelyn after she died of old age, not even fully aware when a younger Evelyn came to see him in the Tower. He was eventually exterminated by the last surviving Dalek when it came to ask him for orders as it didn't know what else to do with itself. (AUDIO: Jubilee)

During the fight with the Lamprey, several alternate Doctors were travelling with different companions, such as Evelyn Smythe, a half cyber-converted Evelyn Smythe, Frobisher, a human/Silurian hybrid Melanie Baal, and Peri Brown. One Doctor, hailing from a timeline where Rome never fell, lost his left eye in the events that led to the death of his companion Perpugilliam of the Brown, keeping the injury as a reminder of his shame. (PROSE: Spiral Scratch)

Adventures that were wiped from history
Before meeting Frobisher, the Doctor travelled with William. (PROSE: Gone Fishing, Walkin' City Blues, Certificate of Destruction, The Earwig Archipelago) These events were undone by the Eighth Doctor in order to stop Flora Millrace embarking on her murder spree. (PROSE: DS Al Fine)

Facing the final curtain
The Doctor tried to travel to the Lakertyan System, but discovered there was deadly radiation nearby and quickly fled, attempting to take Mel to Zastros 8, but instead ending up on Zastros 9, a totalitarian state, and becoming caught up in another situation they only narrowly escaped from when the planet's denizens set chase after them. Back on board his TARDIS, the Doctor found the underside of the TARDIS console smoking. As he went to examine the problem, his consciousness was suddenly transported to the Matrix, and the Valeyard took over his body. Inside the Matrix, the Doctor met a Gallifreyan technician named Genesta, who warned him he was dying. He eventually discovered her to be the Valeyard in disguise.

Throughout their climactic encounter, the Valeyard taunted the Doctor, informing him that he had effectively used creatures called Nathemus to replace the entire Time Lord civilisation with his consciousness and implanted them inside the symbiotic nuclei of the TARDIS. Since the Nathemus fed off telepathic energy, they gained access to its telepathic link, and by extension, the Doctor's mind when he interacted with his ship symbiotically, which let them feed until they were able to gain access to the Matrix, giving the Valeyard a means to take it over and alter history. Because of this, both the Doctor and his TARDIS were now empowering the Nathemus and subject to their influence.

Having been completely defeated in the present, the Doctor realised the only way to break the parasitic hold the Nathemus had on him would be to put a halt to the Valeyard's master scheme in the past. He sent himself a psychic signal via a telepathic impulse from his own TARDIS to go to Lakertya regardless of the danger and experience the deadly radiation, believing he would die if he did so. Suddenly put in a threatened position, the Valeyard tried to convince the Doctor not to go with his plan, but the Doctor carried on, readying himself for the end by reminiscing of all the companions he had during his lifetime. The Valeyard challenged him with the fact that if he didn't die, but regenerated, the Nathemus would still survive. However, the Doctor knew through the process of regeneration, all the cells in his body would be replaced anew, including those of his mind. The Nathemus were linked to the unique mind he had in his present state, but with his mind reshaped, the Nathemus would no longer have any connection with him to feed on it or subsequently manipulate the TARDIS, starving them to death.

After sending his past self the message, therefore undoing all the damage the Valeyard managed to inflict on history, the Valeyard found himself reduced to a powerless form in the Matrix, cut off from the universe and left to shrivel up and die, though it also meant the end for the Sixth Doctor as well. His consciousness began to wane in the wake of time being rewritten, and he sensed the change occurring. (AUDIO: The Brink of Death)

Casting
In 1983, Sylvester McCoy put his name forward in consideration for the Sixth Doctor. . He would later be cast as the Seventh Doctor and briefly played the Sixth Doctor in a regeneration sequence.

Circumstances
Colin Baker declined an invitation to film the regeneration sequence at the start of Time and the Rani due to the circumstances of his dismissal from the role. Wishing to play the Doctor for the whole of Season 24, he was instead offered one last full story to reappear and regenerate. Baker declined, reasoning that he did not want to make the audience think he was still the de facto Doctor for a sliver of 1987 when he had been removed from the series. His successor, Sylvester McCoy, donned a blonde wig and briefly appeared on screen as the unconscious sixth Doctor. McCoy's face was obscured from camera view, first by the TARDIS console and then by the regeneration FX, before the final reveal of the Seventh Doctor. McCoy thus became the first actor to play more than one incarnation of the Doctor. Paul McGann would later play both the Eighth Doctor and the War Doctor in the final moments of The Night of the Doctor (again with his face obscured by the camera placement). Also, Tom Baker has played both the Fourth Doctor and The Curator, though it is not completely confirmed that the Curator is, in fact, a future regeneration of the Doctor.

Following this, Colin Baker did not personally enjoy an official regeneration story until 2015, when he was approached to perform one in audio format, The Sixth Doctor: The Last Adventure. It provides an anthology of four stories spread out across various points in his Doctor's lifetime that are far distanced from each other in the grand scheme of the Sixth Doctor's life, but all play a part in ultimately setting the stage for his Doctor's sendoff, as a complex scheme by The Valeyard to take the Doctor's place via resources acquired across the universe forces the Sixth Doctor to trigger his own regeneration to prevent the Valeyard subverting his timeline. It also made Colin Baker, along with Paul McGann, one of two actors who played the Doctor to receive belated regeneration stories, and including John Hurt in that lineup as the War Doctor, whose introduction and regeneration were both deliberately done in a retroactive manner, one of three actors which portrayed the Doctor whose regeneration took place anachronistically.

The "bang on the head" myth
Due to lack of any information as to what caused the Sixth Doctor to regenerate, viewers were left to draw their own conclusions. At some point, it became the subject of ridicule that the Doctor had regenerated because he hit his head in some manner, an idea which some writers ran with, while others teased it. Some fans even joked it was because he fell off the exercise bike Mel had been forcing him to use since Terror of the Vervoids- the very subject was brought before Colin Baker himself, as evidenced by a YouTube video entitled "Colin Baker Reacts to his Regeneration (50th Anniversary Convention)" by MrTARDISreviews, which shows Baker found it disappointing.

Spiral Scratch by Gary Russell gives a "revisionist" account of the circumstances behind the Doctor's regeneration, explaining that it had not happened simply because he had hit his head, but was drained of the time-based life force that sustained him. Love and War by Paul Cornell offered a different explanation, indicating the Seventh Doctor had willed himself into existence by influencing the Sixth Doctor's demise.

The Brink of Death by Nicholas Briggs, a radiation lethal to Time Lords is the reason behind the Sixth Doctor's end. However, it did not appear to factor in the infamous "bang on the head" as an event coinciding with the Doctor's regeneration in any explicit way due to the fact it is not mentioned through dialogue nor possible to tell if the Doctor hit his head because there is no visual indicator of such a thing happening in the story. However, the Doctor is heard screaming in agony after being buffeted from a strong burst of radiation while a violent crashing sound is audible, proving he suffered some kind of physical trauma. Furthermore, though the Doctor soon afterwards collapses to the floor, there is no evidence of him hitting his head on the way down. It also seems to pull elements from Spiral Scratch and Love and War in terms of spoken dialogue and plot, as well as a charity publication by the late Craig Hinton and associates, Time's Champion.

If anything, the Doctor is either recalling his regeneration inaccurately or generalising it. The former is possible because not only does the stressful process of regeneration often hamper the Doctor's mind and ability to remember things correctly, the Seventh Doctor was subjected to a heavy dose of an amnesia-inducing drug by the Rani not long after regenerating that may have jumbled some of his memories in a lasting manner even after it was out of his system. Moreover, Mel did not witness him regenerate or learn why exactly he did so, robbing both of them of credible accounts of the regeneration. In addition, the latter becomes a possibility as the Doctor is known to lie, make light of events in a dismissive and/or joking manner and even make up things as he goes along as the Tenth Doctor later admitted in The Age of Steel, which further blurs the lines regarding the alleged and contested hit to his head.

Other matters

 * According to an interview with Colin Baker in DWM 118, the Doctor's coat was created because John Nathan-Turner had the idea that it should be in "very bad taste" to show the Doctor's alien nature. Baker himself had wanted to wear black to display the Doctor's darker side.
 * More recently, Colin Baker has expanded upon this, stating that what he wanted to wear was pretty much what would become the costume for Christopher Eccleston's Ninth Doctor. (DOC: Doctor Who: The Ultimate Guide)
 * In AUDIO: The Curse of Davros, the Sixth Doctor was played by Terry Molloy as the Doctor switched bodies with Davros in an attempt to reform the Daleks. A similar event occurred in AUDIO: The Widow's Assassin, when the Doctor is portrayed for a time by Nicola Bryant, as the Doctor briefly transfers himself into the body of his companion Peri Brown to help her expel a neural parasite, correctly assuming that he will be better equipped to suppress the parasite than Peri.
 * Colin Baker related the character of the Doctor to a quote from Rudyard Kipling "I am the Cat who walks by himself, and all places are alike to me". This made him decide to wear a different cat badge on his costume in each story arc. He subsequently received a lot more cat badges from fans in the mail. When he played the Doctor on stage in 1989 these gifts gave him the opportunity to wear a different badge in every single performance.
 * The prose version of the character is one of few incarnations besides the Eighth who has technically crossed with the mythology of Faction Paradox and the War in Heaven. These instances are:
 * The Quantum Archangel, where Faction Paradox is mentioned and the Doctor experiences a timeline similar to the War. Craig Hinton's original notes for the novel, eventually published in the charity publication Shelf Life, asserted the War was negatively affecting the Six-Fold Realm of the Guardians. Hinton and Chris McKeon's Time's Champion utilised those notes and asserted the Sixth Doctor's regeneration, as well as the Seventh Doctor's role as Time's Champion, was due to the coming War.
 * Lawrence Burton's The Time Wrestlers, published in Obverse Books' A Target for Tommy, where the Doctor, Peri, and Señor 105 face War-time agents of the Great Houses. This story loosely connects to Burton's novel Against Nature. The biodata virus from Interference - Book Two is mentioned.