regeneration.

About regeneration

The Time Lords are a fictional ancient race of extraterrestrial people in the British science fiction television series Doctor Who. In-universe, they hail from the planet Gallifrey and are stated to have invented time travel technology. They have sworn an oath to not interfere in the universe; those who reject this and leave the planet to live in the universe are referred to as "renegades". One of their number, the Doctor, fled Gallifrey, stealing one of their time machines known as a TARDIS. In the early days of the series, the Time Lords were not initially referred to, and though the Doctor was stated to be non-human, the character did not clarify beyond that. The Time Lords, as well as the Doctor's affiliation with them, first appeared in the 1969 serial The War Games. Following this appearance, the Time Lords serve as recurring characters, with many individual Time Lords serving either antagonistic or supporting roles in the series. Following the show's 2005 revival, it is revealed the Time Lords had been wiped out in-universe, killed by the Doctor during the events of a war against a species known as the Daleks. Though the Doctor is later able to go back and save the Time Lords in the 2013 episode "The Day of the Doctor", they are killed again by the antagonist the Master during the events of the 2020 episode "Spyfall".