The Sixth Doctor was first seen briefly at the end of "
The Caves of Androzani" (1984), where the
Fifth Doctor, having resisted
regeneration throughout the latter half of the story, finally succumbs to his injuries and transforms into his latest incarnation. Due to the circumstances of his prior iteration's death, the Sixth Doctor suffers from post-regeneration trauma in his debut "
The Twin Dilemma" (1984), where he acts out erratically, seen in his strangulation of companion
Peri Brown, who he accuses of being an "
alien spy". Unaware of what he'd done, but consumed with guilt as he witnesses the newfound terror felt towards him by Peri, the Doctor vows to "become a hermit" on the asteroid of Titan III, only to meet the lone survivor of a crashed ship and a mysterious dome on the asteroid's surface when they arrive. The Doctor and Peri go on to uncover and stop a conspiracy by a member of an alien species known as the Gastropods to
hypnotise a pair of super-intelligent adolescents, who they'd planned to use to advance their nefarious goals; at the end of the story, the Doctor reassures Peri that, through the course of their debut adventure, he'd since fully recovered from his earlier bout of madness, confidently insisting "I
am the Doctor – whether you like it…or not!" He went on to encounter many old foes including the
Master,
Davros and the
Daleks,
Cybermen, and the
Sontarans, and shared an adventure with his own
second incarnation in "
The Two Doctors" (1985). He also faced a renegade female
Time Lord scientist, the
Rani, who had been conducting experiments on humans using the
Luddite riots as a cover. The Doctor and Peri would later land on the devastated planet Ravolox in "
The Mysterious Planet" (1986), which they discovered to actually be Earth, moved across space by unknown forces, resulting in devastating consequences. On a separate adventure, the
TARDIS landed on Thoros Beta, where they confronted the villainous Sil, previously encountered in "
Vengeance on Varos" (1985). What actually occurred here is left intentionally unclear, but initial accounts suggested that Peri was killed after being cruelly used as a test subject in
brain transplant experiments, which the Doctor was stopped from preventing after having been pulled out of time by the Time Lords to face trial under the prosecution of the
Valeyard. In reality, the trial was a cover-up organised by the High Council, sparked in reaction to an alien race from the
Andromeda Galaxy stealing Time Lord secrets and hiding them on Earth; in an effort to dispose of the evidence, the Time Lords renamed Earth to Ravolox, moved it through space, and scorched the surface in a massive fireball, which the Doctor unknowingly uncovered much to his outrage. As the trial continued, the Valeyard would be unmasked as an alternate, evil incarnation of the Doctor, who was an amalgamation of his darkest traits extracted between the Doctor's
twelfth and final incarnations. Also revealed was the Valeyard had been
tampering with evidence shown during the trial, specifically the recordings of the Doctor's travels; in reality, Peri had survived the events of "
Mindwarp" (1986), and went on to marry an alien warrior king she'd met during the events of the story. The trial tangled the Doctor's timeline slightly, as he left in the company of future companion
Mel Bush, a fitness enthusiast from
Pease Pottage, whom he technically had not met yet.
Expanded media Expanded media focusing on the Sixth Doctor often took advantage of the ambiguous space left between his last appearance in "
The Ultimate Foe" (1986) and his unseen death leading into regeneration at the beginning of the
following season, although aspects of the Sixth Doctor preceding the trial have similarly been explored. Following the events of the trial, novels featuring the Sixth Doctor frequently referenced his fear in becoming the Valeyard.
Time of Your Life states that the Doctor went into a self-imposed exile to avoid becoming the Valeyard, Later audio dramas produced by
Big Finish saw the Sixth Doctor make several new companions, including history lecturer
Evelyn Smythe, "Edwardian adventuress" Charley Pollard (a former companion of the
Eighth Doctor, rescued by the Sixth as part of a temporal paradox), supermarket check-out girl Flip Jackson, and
WREN code-breaker Constance Clarke. Several pieces of expanded media, including the 1993 charity special
Dimensions in Time, the novel
The Shadow in the Glass, and the audio play
The Spectre of Lanyon Moor, have portrayed the Sixth Doctor working with his old friend
Brigadier Lethbridge-Stewart. Frobisher, a
shapeshifting alien often taking the form of a penguin, first originated in
Sixth Doctor comic stories beginning in 1984 as a companion of his and has further appeared with the Doctor in audio plays.
Death and regeneration Several different and conflicting accounts of how the Sixth Doctor died at the beginning of "
Time and the Rani" (1987) exist in an attempt to fill the gap left by the episode's vague nature in how it was portrayed.
Pip and Jane Baker's novelisation of the episode provides the first relatively brief attempt to explain the Doctor's regeneration (specifically, that it was triggered by "tumultuous buffeting" as the Rani attacked the TARDIS). The
Virgin New Adventures series suggests that the
Seventh Doctor somehow deliberately killed the Sixth, because he could not become the master-planner and manipulator that his next incarnation became, due to his fear of becoming the Valeyard. The
BBC Books Past Doctor Adventures novel
Spiral Scratch proposes that the Sixth Doctor died as a result of his chronal energy being drained in a confrontation with a powerful pan-dimensional entity before being snared by the Rani's beam. In 2015, Big Finish released
The Sixth Doctor: The Last Adventure, an audio drama depicting the events leading up to the Sixth Doctor's death and regeneration. the Valeyard regained enough of his energy after their last battle to have essentially 'replaced' the Doctor, thanks to him having planted parasitic creatures in the TARDIS's telepathic circuits, allowing him to trap the last fragments of the Doctor's personality in the Matrix (the
supercomputer of the Time Lord High Council). To undo the damage created by the Valeyard, who has already begun to replace portions of the Doctor's timeline, the Doctor sends a message out from the Matrix to his own past self in a bid to divert the younger Doctor's trajectory and prevent the Valeyard's victory. As a result, the younger Doctor is exposed to a lethal dose of radiation, with his death and subsequent regeneration killing the parasites, stopping the Valeyard from succeeding, but consequently killing him in the process. ==Costume==