companion

In the long-running BBC television science fiction programme Doctor Who and related works, the term "companion" refers to a character who travels or shares adventures with the Doctor. In most Doctor Who stories, the primary companion acts as an audience surrogate. They provide the lens through which the viewer is introduced to the series. The companion character often furthers the story by asking questions (often to help the audience understand too) and getting into trouble; also by helping, rescuing, or challenging the Doctor. This designation is applied to a character by the show's producers and appears in the BBC's promotional material and off-screen fictional terminology. The Doctor also refers to the show's other leads as their "friends" or "assistants"; the British press have also used the latter term.