Every transformation from one Doctor to the next — the causes, the episodes, and the stories behind each regeneration across the full history of Doctor Who.
The Second Doctor was put on trial by the Time Lords for stealing a TARDIS and repeatedly meddling in the affairs of other civilisations. Found guilty, he was forced to regenerate into a new body and exiled to twentieth-century Earth — a sentence that stripped him of his freedom and his companions.
The Third Doctor sacrificed himself to retrieve the Great Crystal from the planet Metebelis Three, absorbing a fatal dose of radiation from the giant spiders in the process. His old friend K'anpo Rimpoche — a Time Lord monk — helped trigger the regeneration, and the Doctor collapsed in the TARDIS before transforming into his fourth incarnation.
After preventing the Master from holding the universe to ransom using the Pharos Project's transmitter, the Fourth Doctor fell from a great height. As he lay dying, the Watcher — a mysterious pale figure who had accompanied him throughout the adventure — merged with him, and he regenerated into the Fifth Doctor surrounded by his companions.
The Fifth Doctor and his companion Peri both contracted spectrox toxaemia while trapped in the caves of Androzani Minor. With only enough antidote for one, the Doctor gave all of it to Peri and perished. Widely regarded as one of the most emotionally powerful regenerations in the show's history, it is remembered for the Doctor's dying vision of his companions urging him to fight for survival.
The Sixth Doctor's regeneration was never depicted on screen — the circumstances were established in expanded media and the opening of the following serial. The Rani attacked the TARDIS mid-flight, causing it to crash. The Doctor was found unconscious and regenerated off-screen into the Seventh Doctor, who the Rani then impersonated to pursue her own schemes.
Landing in San Francisco on the eve of the millennium, the Seventh Doctor was caught in gang crossfire and shot. He survived initial surgery but was mistakenly operated on by a cardiac surgeon unaware of his alien physiology, triggering a catastrophic interruption of the regeneration process. He eventually regenerated in the hospital morgue, emerging as the Eighth Doctor.
The Eighth Doctor died when his stolen spaceship crashed on the planet Karn during the early Time War. Brought back briefly by the Sisterhood of Karn, he chose to drink a potion that would allow him to regenerate into a warrior — not a Doctor — to fight in the Time War. With the words "Physician, heal thyself," he became the War Doctor, rejecting the name entirely until it was reclaimed centuries later.
The First Doctor's body simply wore out after years of travel. Collapsing in the TARDIS, he transformed into a younger, more energetic incarnation.
After helping to save Gallifrey rather than destroy it during the final day of the Time War, the War Doctor's ancient, battle-worn body gave out. As he dematerialised alone in the TARDIS, he remarked "I hope the ears are slightly less conspicuous this time" before regenerating into the youthful Ninth Doctor — finally deserving the name of the Doctor once more.
Facing a Dalek fleet that threatened the obliteration of Earth and the entire universe, Rose Tyler absorbed the full power of the Time Vortex from the heart of the TARDIS and destroyed the Dalek Emperor's forces. The energies were killing her, and the Ninth Doctor took the Vortex into himself to save her — an act of self-sacrifice that triggered his regeneration into the Tenth Doctor.
Forced into a trap set by the resurrected Master and a rogue Time Lord faction, the Tenth Doctor ultimately saved Wilfred Mott by absorbing a massive radiation surge inside a glass booth. He then took time to say farewell to each of his companions across time before finally collapsing in the TARDIS — his last words, "I don't want to go," among the most poignant in the show's history.
The Eleventh Doctor spent hundreds of years defending the town of Christmas on the planet Trenzalore against a coalition of enemies, growing old in the process. The Time Lords, hearing the question "Doctor who?" through a crack in the universe, granted him a brand-new regeneration cycle. Reinvigorated, he unleashed a regenerative energy burst that destroyed the Dalek fleet before transforming into the Twelfth Doctor.
The Twelfth Doctor initially resisted regeneration after being wounded, and encountered his own first incarnation — who was equally reluctant to change. Through a shared adventure involving a World War One soldier and a mysterious glass avatar, both Doctors found their resolve. The First Doctor departed to complete his own regeneration, and the Twelfth finally embraced the change, leaving words of hard-won wisdom for his next self before transforming into the Thirteenth Doctor.
In a stunning multi-enemy assault, the Master forced the Thirteenth Doctor to regenerate into a copy of himself aboard the Citadel of Gallifrey, assisted by renegade Cybermen and the Daleks. Former companions rallied to help reverse the process and restore the Doctor. Returning to herself, the Thirteenth Doctor said her farewells to old friends before completing her regeneration — transforming into the Fourteenth Doctor, wearing a surprisingly familiar face.
After the Celestial Toymaker used a "giggle" signal to drive the entire human race into conflict, the Fourteenth Doctor defeated him in a tense game of catch. The Toymaker's parting shot triggered a bi-generation — an extremely rare event — splitting the Doctor into two simultaneous incarnations: the Fourteenth and the Fifteenth. Rather than one replacing the other, both Doctors existed at once, with the Fourteenth choosing to rest and heal alongside Donna Noble's family.