Fourteen actors have portrayed the Doctor in a leading role in the British science fiction television series Doctor Who. The series' protagonist, the Doctor is an extraterrestrial Time Lord. The transition to each succeeding actor is explained within the narrative through the plot device of regeneration, which allows Time Lords a change of cellular structure and appearance. The first actor to portray the Doctor was William Hartnell beginning with An Unearthly Child (1963) through The Tenth Planet (1966). In the final moments of "The Tenth Planet", the First Doctor regenerated into Patrick Troughton's Second Doctor.
The incumbent Fifteenth Doctor is played by Ncuti Gatwa, who took over the role from David Tennant following the conclusion of "The Giggle" (2023).
Outside of television many actors have played the Doctor on in various BBC-licensed spin-offs on television, stage, radio, film, audio plays, and webcasts. The character's ability to periodically regenerate appearance and personality has facilitated the ability of new actors to take over the role – in official and unofficial productions – while in most cases maintaining continuity with the television series. Several other actors have also been considered for the role.