Thomas Stewart Baker (born 20 January 1934) is an English actor. He is best known for his portrayal of the fourth incarnation of the Doctor in the science fiction series Doctor Who from 1974 to 1981, a longer tenure than any other actor, and for the narration of the comedy series Little Britain. Baker's voice, which has been described as "sonorous", was voted the fourth-most recognisable in the UK.

At the age of 15 Baker began study as a religious brother. However, he gradually lost his vocation and at 21 he left religious life and undertook National Service in the Royal Army Medical Corps. On leaving the army, he joined the Merchant Navy and then became an actor, joining the Royal National Theatre Company under Laurence Olivier.

Baker was in his thirties when his professional acting career began, and his first major film role was as Grigori Rasputin in Nicholas and Alexandra in 1971, when he was 37. He went on to play the villainous Prince Koura in The Golden Voyage of Sinbad in 1973, which led to his casting in Doctor Who. During his period as its star, the series was distinguished by high viewing figures and many stories which became regarded as classics. He remains one of the most instantly recognisable incarnations of the character. He continued to win regular roles in TV later in his career, most notably in the series Medics and Monarch of the Glen. In addition to performing acting roles, Baker has narrated commercials, video games, audiobooks and television series.

In a poll for the BBC Homes and Antiques magazine in January 2006, Baker was voted the world's fourth-most eccentric star. He was beaten by Björk, Chris Eubank and David Icke. Married three times, the second to Doctor Who co-star Lalla Ward, Baker has two sons from his first marriage.