The Second Doctor is an incarnation of the Doctor, the protagonist of the British science fiction television series Doctor Who. He was portrayed by actor Patrick Troughton. 53 of his 119 episodes are missing.

The Doctor is the protagonist of the long-running BBC science fiction television series Doctor Who. They are an extraterrestrial Time Lord who travels the universe in a time travelling spaceship, called the TARDIS, often with companions. Since the show's inception in 1963, the character has been portrayed by fourteen lead actors. The transition to each succeeding actor is explained within the show's narrative through the plot device of regeneration, a biological function of Time Lords that allows a change of cellular structure and appearance with recovery following a mortal injury.