The Doctor (Doctor Who)
The Doctor is the title character in the long-running BBC science fiction television programme "Doctor Who". Since the show's inception in 1963, the character has been portrayed by thirteen lead actors. In the programme, "the Doctor" is the alias assumed by a centuries-old alien—a Time Lord from the planet Gallifrey—who travels through space and time in the TARDIS, frequently with companions. The transition to each succeeding actor is explained within the show's narrative through the plot device of "regeneration", a biological function of the Time Lord race that allows a change of cellular structure and appearance with recovery following a potentially fatal injury.
Twelfth Doctor
The Twelfth Doctor is an incarnation of the Doctor, the protagonist of the BBC science fiction television programme "Doctor Who". He is portrayed by Scottish actor Peter Capaldi. Within the series' narrative, the Doctor is a time travelling, humanoid alien from a race known as the Time Lords. At the end of life, the Doctor can regenerate his body, and in doing so gain a new physical appearance, and with it a distinct new personality; this plot mechanism has allowed the Doctor to be portrayed by a series of actors over the decades since the programme's inception in 1963. Capaldi's portrayal of the Doctor is a spiky, brusque, contemplative, and pragmatic character who conceals his emotions in the course of making tough and sometimes ruthless decisions.