Sixth Doctor

Classic Series
The Fifth Doctor regenerated after contracting the fatal disease spectrox toxaemia on Androzani Minor, having given the only antidote to save his companion Peri. He remarked in his final moments that the regeneration felt "different", and only an act of will spurred on by hallucinations saved him from death. From these troubled beginnings sprang the Sixth Doctor, who initially suffered from several psychotic symptoms in the period directly following the regeneration. Eventually he stablised as an outwardly arrogant buffoon, but he was just as capable of compassion and violence as his predecessor.

He travelled with Peri - and sometimes the Whifferdil shapeshifter, Frobisher - until he stumbled, alone, out of the TARDIS into a space station operated by the Time Lords. Suffering from amnesia, he found himself once again on trial for interfering in the affairs of the Universe. He elected to represent himself in the trial, for which he and his prosecutor, the Valeyard, would present episodes from his life as evidence via the Matrix. Through these he learned that Peri was dead, the subject of foul experiments in brain transplantation, and that he would in his future meet Melanie Bush, a computer programmer from Pease Pottage, Essex. It was eventually revealed that the Valeyard was an evil, possible future version of the Doctor, who had falsified the Matrix evidence - including Peri's fate - with the aid of the High Council, in order to cover up a conspiracy which the Doctor had unknowingly uncovered. In return for securing the Doctor's execution, the Valeyard would have stolen the Doctor's remaining regenerations, beoming a true Time Lord in his own right.

The Doctor defeated the Valeyard and departed with Mel, causing some confusion, as he hadn't met her yet in his own timeline. It is assumed he returned her to his future self, and later met her for the first time, travelling with her until the TARDIS was caught in the Rani's energy beams, crash-landing on Lakertya. This crash landing was apparently enough to spark his regeneration into the Seventh Doctor (though see below).

Expanded Universe
In the novels and audio adventures, it is assumed that the Sixth Doctor has a great many adventures and meets other companions between the end of his trial and his end on Lakertya. He initially spends time lamenting his fate and, fearful of becoming the Valeyard, resolves to become a hermit on the planet Torrok and avoid ever meeting Mel, changing his own future. He is caught up in events there, however, and travels again with a new companion, Grant Markham. (Time of Your Life and Killing Ground, by Steve Lyons)

After parting from Grant on less than friendly terms, he travelled alone, meeting up briefly again with Frobisher, before eventually meeting Evelyn Smythe. He and Evelyn had a deep friendship, each helping the other heal their emotional problems, and when she chose to leave him he was deeply hurt; this may be why he dropped her off on Earth 10 years before she left with him, causing her a lot of trouble. (Various Big Finish audios; Instruments of Darkness, by Gary Russell) The Doctor eventually meets Mel on Earth and, when she stows away in the TARDIS, decides to accept the inevitable. (Business Unusual, by Gary Russell)

Several alternate explanations are also given for the Sixth Doctor's regeneration, which seemed unwarranted given the severity of the crash. One theory suggests that the Doctor subconsciously sacrificed his sixth self so he could be reborn as Time's Champion. The Sixth persona's anger over this is suggested as the psychological cause for the Valeyard's evil. (Love and War, by Paul Cornell) Another theory is that the Doctor had been injured or poisoned, and was already dying; the crash just finished him off. (Spiral Scratch, by Gary Russell)

Characteristics
The Sixth Doctor is probably the most consistently arrogant, and certainly the most bombastic. He almost never doubted his own ability, and considered himself greatly superior to nearly everyone he encountered. This included his companions, especially Peri, though he seemed to have mellowed during his time with Evelyn. More than his other incarnations, the Sixth Doctor could be something of a fatalist, more than once deciding he was doomed and resolving to accept his fate.

Physically, he is very tall; Mel also considered him to be overweight, and forced him to take up both a diet (consisting mainly of carrot juice) and an exercise regime, neither of which he felt he needed.

Personality
The Sixth Doctor was unpredictable in every sense of the word. Arrogant and self-absorbed, stubborn and childish, argumentative and tasteless, he could often be seen as unlikeable or even loathesome. This was a Doctor who did not suffer fools gladly; he sometimes seemed to endure his companion's presence far more than he actually appreciated it, and held himself as superior to almost anyone he encountered. But the new incarnation's brash exterior hid the fact that this was a Doctor more determined than ever to defeat the evil he encountered. He was possessed of a tenacity and a thirst to do what was right that was far more visible than ever before. Despite his often unstable demeanour, he was always quick to act when the situation called for it, and very little -- even his companions -- could hope to get in his way.

Habits and Quirks
The Sixth Doctor is very fond of cats, and always wears one of a number of cat-shaped pin or brooches in his possession. His taste in clothes is the subject of much ridicule, though it has been suggested that he wears his outlandish coat in order to distract people from noticing anything else about him.

Mysteries and Discrepancies

 * Why is he so much more erratic than the other Doctors immediately following his regeneration? Is spectrox toxaemia really so severe as to provoke such a reaction in a Time Lord?


 * Why does he leave with Mel at the end of his trial? Surely, even if he is taking her back to her proper place with his future self, that would floout the Laws of Time right under the Time Lord's noses?


 * Perhaps the Law of Time work differently than the way we had assumed.


 * We have varying accounts of the reason for this Doctor regenerating into his next form besides the simple of a head injury.

Undocumented adventures

 * The Doctor had met Captain Travers previously. (DW: Terror of the Zyons)

Key Life Events

 * The Doctor regenerates. (DW: The Caves of Androzani)


 * The Doctor re-unites with Jamie and encounters his own second incarnation. (DW: The Two Doctors)


 * The Time Lords put the Doctor on trial and serves as his own defender. The Valeyard is his prosecutor and also his own possible future incarnation. (DW: The Trial of a Time Lord).


 * The Doctor regenerates. (DW: Time and the Rani)