Main cast •
Tom Baker as the
Fourth Doctor •
Elisabeth Sladen as
Sarah Jane Smith •
Ian Marter as
Harry Sullivan During production of season eleven, it was known that
Jon Pertwee would be leaving his role as the
Third Doctor and that a new
Fourth Doctor would need to be cast for the part.
Tom Baker was an out-of-work actor, working in construction at the time. Baker had been a television and film actor, having major parts in several films including
The Vault of Horror (1973) and as the main antagonist in
The Golden Voyage of Sinbad the same year. He had written to Bill Slater, the Head of Serials at the BBC, asking for work. Slater suggested Baker to
Doctor Who producer
Barry Letts who had been looking to fill the part. Letts had been the producer of the series since the early Pertwee serials in 1970. He had seen Baker's work in
The Golden Voyage of Sinbad and hired him for the part. Baker would continue in his role as
the Doctor for seven seasons, longer than any other actor to play the part.
Elisabeth Sladen returned to play the role of companion
Sarah Jane Smith throughout the season.
Ian Marter joined the cast as
Harry Sullivan. The character was created before Baker was cast; there had been discussion of casting an older actor as the Doctor, and so Harry was created as a younger character to handle the action scenes.
Recurring cast •
Nicholas Courtney as
Brigadier Lethbridge-Stewart •
John Levene as
Warrant Officer Benton Nicholas Courtney and
John Levene reprised their roles as
the Brigadier and
Warrant Officer Benton respectively in the first serial,
Robot. Courtney had begun his role in the
Second Doctor story
The Web of Fear (1968), where the character was a colonel. Levene had begun in
Second Doctor story
The Invasion (1968), replacing another actor. Both were members of the military organization
United Nations Intelligence Taskforce (UNIT). They, along with Sladen, would be the transition cast to carry through from the Third Doctor to the Fourth Doctor, though
Robot is the only UNIT story for the twelfth season. == Serials ==