William Henry Hartnell was an English actor, who is best remembered for his portrayal of the First Doctor, the original on-screen 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 First Doctor is the original incarnation of the Doctor, the protagonist of the British science fiction television series Doctor Who. He was portrayed by actor William Hartnell in the first three series from 1963 to 1966 and the tenth anniversary story The Three Doctors from 1972 to 1973. The character would occasionally appear in the series after Hartnell's death, most prominently as portrayed by Richard Hurndall in the 1983 multi-doctor special The Five Doctors, and as portrayed by David Bradley in the 2017 Twelfth Doctor episodes "The Doctor Falls" and "Twice Upon a Time" and in the 2022 Thirteenth Doctor episode "The Power of the Doctor", the latter previously having portrayed Hartnell himself in the 2013 biopic An Adventure in Space and Time.