First Doctor

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 occasionally appeared in the series after Hartnell's death, played by Richard Hurndall in the 1983 special "The Five Doctors" and by David Bradley in 2017 and 2022. To date, the First Doctor is the sole incarnation of the Doctor to have been recast for later televised appearances.

Within the series' narrative, the Doctor is a centuries-old alien Time Lord from the planet Gallifrey who travels in time and space in the TARDIS, frequently with companions. At the end of life, the Doctor regenerates; as a result, the physical appearance and personality of the Doctor changes. The concept of regeneration, initially referred to as a "renewal", was introduced when Hartnell left the series due to his increasingly bad health, consequently extending the series' life into the following century, with Hartnell being succeeded by the Second Doctor (Patrick Troughton).

Hartnell's portrayal of the character was initially a stubborn and abrasive old man who was distrustful of humans, but ultimately mellowed out into a more compassionate, grandfatherly figure who adored his travels with his companions. The First Doctor's original companions were his granddaughter Susan Foreman (Carole Ann Ford) and her schoolteachers Ian Chesterton (William Russell) and Barbara Wright (Jacqueline Hill). In later episodes, he travelled alongside 25th-century orphan Vicki (Maureen O'Brien), space pilot Steven Taylor (Peter Purves), Trojan handmaiden Katarina (Adrienne Hill), and sixties flower child Dodo Chaplet (Jackie Lane). His final on-screen companions were the working class sailor Ben Jackson (Michael Craze) and the sophisticated socialite Polly (Anneke Wills). Of the 134 episodes Hartnell appeared in as a regular, 44 are missing.