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The causes of regeneration, especially amongst Time Lords, were many and varied. They ran the gamut from simple desire to change, to life-threatening maladies which typically resulted in human death. The following are the known causes of regeneration of specific Time Lords.
The Doctor
This chart considers regeneration to be something which results in an actual, irreversible transformation from one body to another. Things like the Tenth Doctor's accidental creation of the Meta-Crisis Doctor, or the reversal of regeneration in The Touch of the Nurazh, are not included here, even though the former is acknowledged in The Time of the Doctor as counting as a full regeneration. Also not considered here are Doctors from alternative timelines.
| Doctor | Reason | Story | |
|---|---|---|---|
| 1 | Claimed to be "wearing a bit thin"; apparently died of simple old age, but other accounts suggest he also had his waning life force pulled out of him by the planet Mondas. | The Tenth Planet | File:First Doctor regenerates - William Hartnell to Patrick Troughton |
| 2 | Forced to change his appearance by Time Lord court order, and eventually executed by animated scarecrows. | Sentence passed in The War Games, carried out in The Night Walkers | 
|
| 3 | Radiation poisoning upon exposure to The Great One's highly unstable web of Metebelis crystals. | Planet of the Spiders | File:Third Doctor regenerates - Jon Pertwee to Tom Baker - BBC |
| 4 | Fell to the ground from great height at the Pharos Project; indirectly caused by the Tremas Master. | Logopolis | File:Fourth Doctor regenerates - Tom Baker to Peter Davison - BBC |
| 5 | Refusal to take antidote for spectrox toxaemia in order to give it instead to Peri Brown, succumbing to the fatal effects of the poisoning. | The Caves of Androzani | File:Fifth Doctor regenerates - Peter Davison to Colin Baker - BBC |
| 6 | Ambiguous injury consequent to the Rani's attack on the TARDIS. Some accounts indicated the Doctor hit his head on the TARDIS console. Others suggest that he was also suffering from a chronal energy drain after his confrontation with the Lamprey and this served as the killing blow. | Time and the Rani (explained in Head Games, Spiral Scratch) | File:Sixth Doctor regenerates - Colin Baker to Sylvester McCoy - Doctor Who Time and the Rani - BBC |
| 7 | Following a non-fatal shooting, the Seventh Doctor underwent open heart surgery in a San Francisco hospital. Since the attending cardiologist had no knowledge of Time Lord physiology, she accidentally killed him. | Doctor Who | |
| 8 | Died after a ship he was in crash-landed on Karn; temporarily resurrected to consume the Sisterhood of Karn's Elixir of Life and control his next regeneration for the Last Great Time War. | The Night of the Doctor | 
|
| War | As with the First Doctor, he claimed to be "wearing a bit thin" and regenerated from what appeared to simply be old age. | The Day of the Doctor | 
|
| 9 | Directly absorbed time vortex energy from the Bad Wolf to save the life of Rose Tyler. | The Parting of the Ways | File:Ninth Doctor regenerates - Christoper Eccleston to David Tennant - Doctor Who - BBC |
| 10 | Intentional radiation poisoning incurred in order to save the life of Wilfred Mott. | The End of Time | File:The Tenth Doctor Regenerates - David Tennant to Matt Smith - Doctor Who - BBC |
| 11 | As with the First and War Doctors, his body succumbed to old age, but by a far greater amount than either of them. This marked the beginning of a new regeneration cycle granted by the Time Lords. | The Time of the Doctor | File:The Eleventh Doctor Regenerates... The Twelfth Doctor Appears! - Doctor Who Christmas Special - BBC |
Romana
- First to second incarnation: Decided it was time for a change, another account said unknown to the Doctor, Romana was harmed by the Key to Time. (TV: Destiny of the Daleks, AUDIO: Lies, The Key 2 Time - The Chaos Pool, PROSE: The Lying Old Witch in the Wardrobe)
- Second to third incarnation: Regenerated in preparation for the Second War in Heaven, developing a body and attitude more suited for combat. (PROSE: The Shadows of Avalon)
- The second incarnation started to regenerate due to contact to the decaying Eye of Harmony inside the Matrix. (AUDIO: Renaissance). This regeneration didn't take hold due to K9 Mark II removing her from the Matrix. (AUDIO: Ascension)
- Third to fourth incarnation: Managed to survive the Second War in Heaven, although this may have entailed a regeneration. (PROSE: Tomb of Valdemar)
The Master
- Shot by Ace after receiving a new set of regenerating nanites from the Tzun. However, these were apparently only effective in the short term. (PROSE: First Frontier)
- During the Last Great Time War, the Time Lords resurrected the Master, apparently giving him a new regeneration cycle in the process (TV: The Sound of Drums) as, when the War Master was shot by Chantho, he regenerated into a new incarnation. (TV: Utopia)
- After being shot by his wife, Lucy Saxon, the Master was able to consciously prevent himself from regenerating. (TV: Last of the Time Lords), though this is later implied to have been a ploy to allow his resurrection at later date (TV: The End of Time). It it not clear if this resurrection can be considered a regeneration or not; although his face remains the same, the Master tells a pair of humans (before killing them) that he is a new Master stuck with the same appearance.
- Note: Other occasions in which the Master has appropriated a new body, (TV: The Keeper of Traken, Doctor Who) are not considered regenerations.
Rassilon
- Rassilon was said to have achieved immortality. (TV: The Five Doctors)
K'anpo Rimpoche
- K'anpo Rimpoche was attacked by the Eight Legs on Earth. He regenerated into the form of Cho Je, a projection of his own mind. (TV: Planet of the Spiders)
Borusa
- Borusa regenerated at least three times, and had at least four incarnations. (TV: The Deadly Assassin, TV: The Invasion of Time, TV: Arc of Infinity, TV: The Five Doctors)
Chronotis
Rallon
- Rallon initiated all twelve of his regenerations to force the Celestial Toymaker out of his body. (PROSE: Divided Loyalties)
Roche
- Lord Roche was caught in a traffic accident while on Earth; he retained enough control over the process after it began to deliberately shape his new appearance so that he was the exact duplicate of the Third Doctor (PROSE: The Suns of Caresh).
Azmael
- In his thirteenth and final body, Azmael regenerated past his limit, killing him and Mestor, who possessed Azmael's body after his own was destroyed. (TV: The Twin Dilemma)
Iris Wildthyme
- Iris Wildthyme regenerated following a lengthy period of illness following the consumption of a live Kaled mutant. (PROSE: The Scarlet Empress)
The War Chief
- The War Chief underwent a faulty regeneration after being shot by War Lords; lack of medical care and the scale of the damage sustained resulted in his new form appearing like two bodies fused together. (PROSE: Timewyrm: Exodus)
The Monk
- The Monk regenerated at least once. (PROSE: No Future, AUDIO: The Book of Kells)
Ruath
- Ruath drained every drop of her blood from her body to restore Vampire Lord Yarven. Yarven subsequently turned her into a vampire. (PROSE: Goth Opera)
Innocet
- Innocet was killed by a Quences-possessed Badger to protect the Doctor (PROSE: Lungbarrow).
I.M. Foreman
- As a priest, I.M. Foreman had been given the gift of regenerations. This made twelve different individuals, who were created by his body absorbing the DNA around him; all regenerations were caused by the Third Doctor sending the first twelve back to Gallifrey's past so that they fell from a great height and regenerated into the next one. (PROSE: Interference - Book One, Interference - Book Two)
The Corsair
- The Corsair regenerated several times, with "a couple" of his incarnations being female. He was back to male by the time he was killed by House. He/she either created or acquired the same snake tattoo in each incarnation. (TV: The Doctor's Wife)
River Song
- First to second incarnation: As a little girl, Melody Pond, later known as River Song, regenerated on the streets of New York City in 1970 due to a terminal illness. (TV: The Impossible Astronaut, Day of the Moon)
- Second to third incarnation: Melody later regenerated in Hitler's private study in 1938 after the Führer accidentally shot her while aiming for the Teselecta. She later used up all of her remaining regenerations to heal the Doctor from a poison with which she had infected him. (TV: Let's Kill Hitler) She later suffered a fatal electric shock when she sacrificed her memory space to save the lives trapped inside CAL. However, the Tenth Doctor uploaded her data ghost to the The Library's supercomputer. (TV: Forest of the Dead)