List of causes of regeneration

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.

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

 * Apparently exhausted most of his lives after being trapped in the event horizon of the black hole powering the Darkheart (PROSE: The Dark Path).
 * Shot by Ace after receiving a new set of regenerating nanites from the Tzun (PROSE: First Frontier). However, these were apparently only effective in the short term, as he was later shown attempting to restore his ability to regenerate using the Sacred Loom of Rassilon's Mouse (PROSE: Happy Endings).
 * During the Last Great Time War, the Time Lords resurrected the Master, giving him a new regeneration cycle in the process (TV: The Sound of Drums) as, when was shot by Chantho, he regenerated into a . (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 is 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, AUDIO: Mastermind) are not considered regenerations.

Rassilon

 * Rassilon was said to have achieved immortality in the form of a "Timeless, perpetual, bodily regeneration." (TV: The Five Doctors) He appeared to have been reduced to a mind within the Matrix (AUDIO: Zagreus), but he was able to manifest a new body in his workshop, and was later restored to full corporeal form to lead Gallifrey in the Time War (PROSE: Engines of War).

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

 * Salyavin used up his thirteenth and final incarnation when he was attacked by the Sphere. However, when his Type 12 TARDIS was sent backwards, it altered his personal timeline and brought him back to life. (HOMEVID: Shada/WC: Shada)

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 after 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, the damage preventing him from ever regenerating again. (PROSE: Timewyrm: Exodus)

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).

Glospin

 * Glospin force-regenerated himself into the double of the Doctor after acquiring a genetic sample to influence the appearance of his next incarnation (PROSE: Lungbarrow).
 * Having killed Quences in 'disguise' as the Doctor, Glospin regenerated again to conceal his role in the murder (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)

Cavisadoratrelundar

 * A Time Lord agent, Cavis nearly regenerated after she was decapitated by Queen Regent Mab, but Mab also stabbed her in both hearts to ensure that she remained dead (PROSE: The Shadows of Avalon).

Gandarotethetledrax

 * A Time Lord agent, Gandar was stabbed in the heart by Mawgryn, but regenerated as Margwyn was unable to impale his second heart (PROSE: The Shadows of Avalon).
 * Gandar regenerated again shortly after his previous regeneration when he received a fatal sword wound; his new incarnation resembled a hybrid of human and Silurian, and was far more peaceful than his previous violent selves (PROSE: The Shadows of Avalon).

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)

Karlax

 * Exposure to the space vacuum after Dalek stealth ships destroyed his Battle TARDIS during the Last Great Time War. (PROSE: Engines of War)