Over the course of its many years on television, the long-running British science fiction television series Doctor Who has not only seen changes in the actors to play the Doctor, but in the supporting cast as well.
The Doctor is usually accompanied in his travels by one to three companions (sometimes called assistants). These characters provide a surrogate with whom the audience can identify, and further the story by asking questions and getting into trouble, (similar to Dr. Watson in the Sherlock Holmes mysteries.) The Doctor regularly gains new companions and loses old ones; sometimes they return home, or find new causes on worlds they have visited. A few of the companions have died during the course of the series.
Many characters have appeared in multiple stories; some of which can also dubiously be considered companions, having travelled on the TARDIS, but not as a main character.
The Doctor Who comics, novels and audio dramas have created companions, villains and supporting characters of their own. Some of these originated in one medium and later appeared in another. The lists below indicate where a character has appeared.
