On Saturday 21 March 1981 actor Tom Baker made his final appearance as
Doctor Who in the long running BBC TV series of the same name.
Baker (b. 1934) began his most famous acting role in June 1974, making him the 'Fourth Doctor', taking over from Jon Pertwee in the final episode of
Planet of the Spiders. He completed his role in the fourth and final episode of
Logopolis in 1981, which introduced Peter Davison as the Fifth Doctor at the very end of the story via the traditional 're-generation' method.
Episodes featuring Davison as the Fifth Doctor began broadcasting in January 1982.
source:
tardis.wikia.com