Doctor Who. Doctor Who - The Official Site. Tardis Data Core, the Doctor Who wiki. Doctor Who TV. Companion (Doctor Who) The character of Harry Sullivan was created by the production team when it was expected that the Fourth Doctor would be played by an older actor who would have trouble with the activity expressed by his predecessor. In the event, the Fourth Doctor part went to 40-year-old Tom Baker and the part of Harry, no longer required for the action role, was reduced.[3] In the final season for the Fourth Doctor, he acquired three companions (Adric, Tegan and Nyssa) and this situation continued under the Fifth Doctor for a while.
Adric was written out by the unusual method within the series of being "killed off". By the Sixth Doctor, the Doctor was down to a single companion again. Although the term "companion" is designated to specific characters by the show's producers, and appears in the BBC's promotional material and off-screen fictional terminology, there is no formal definition that constitutes such a designation.