Regeneration (Time Lord)

A Time Lord has thirteen lives all told; when at the end of one life, they can regenerate into a new body. This is a property unique to Time Lords/Ladies. There have been suggestions that some were able to extend the number of regenerations; however, the only known cases of this are The Master, under unusual circumstances&mdash;twice by taking over a human (or other non-Time Lord) body, and the third time when he was resurrected and given a new set of regenerations by the Time Lords. This was not, on reflection, a very good idea.

PPC Agents who have gone through regeneration include Morgan, The Agent, The Disentangler, and Tawaki Penguin (though not originally a Time Lord).

The Doctor has also been revealed to have been granted an extension in regenerations, as the recent specials have revealed that the Eleventh Doctor has actually expended all thirteen lives. The Eighth Doctor apparently regenerated into the War Doctor (John Hurt), who regenerated into Nine, who regnerated into Ten. Ten regenerated during the season four finale, but managed to keep his current face and caused instead a metacrisis -- but that was still considered a regeneration in the full scheme of things. Therefore to regenerate Eleven into Twelve (Peter Capaldi), the Time Lords of Gallifrey, who had been relocated into a parallel dimension instead of being destroyed and were attempting to contact the prime timeline through cracks in space and time, seemed to have given Eleven a new set of regenerations.