William Henry Hartnell was an English actor, who is best remembered for his portrayal of the First Doctor, the original incarnation of the Doctor, in Doctor Who from 1963 to 1966. In film, Hartnell notably appeared in Brighton Rock (1949), The Mouse That Roared (1959) and This Sporting Life (1963). He was associated with military roles, playing Company Sergeant Major Percy Bullimore in the ITV sitcom The Army Game and Sergeant Grimshaw, the title character in the first Carry On film Carry On Sergeant (1958).

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.