Companion

Over the centuries, the Doctor has acquired numerous companions in his travels through space and time. Some appear to have travelled with him for years, others for just a few days. While these companions have included members of various species from different planets, most have been humans from the planet Earth, especially the 20th and 21st centuries. Most of these, in turn, have been young females. The earliest known companion of the Doctor was Susan Foreman, generally believed to be his granddaughter and a fellow native of Gallifrey. For a full roster of the Doctor's companions, go here.

Other Time Lords have been known to have companions in their travels. Before his final corruption into the renegade known as the Master, the Time Lord Koschei was accompanied in his hunt for the Doctor by Ailla. Koschei believed Ailla to be a young woman from a 28th century Earth colony, but she was in fact a Time Lady agent sent by the High Council to spy on the increasingly erratic Koschei's actions ("The Dark Path"). In his battle with the newly regenerated Eighth Doctor, the Master was assisted by Chang Lee, a young man in 1999 San Francisco. Lee had been convinced by the Master that the Doctor was evil. Only too late did he learn the truth as the Master killed the boy. Fortunately the Doctor was able to reset the timestream when he closed the Eye of Harmony, thus restoring Lee and the Doctor's own companion Grace Holloway back to life ("Doctor Who: The TV Movie").

In her last known battle with the Doctor, the Rani was assisted by a young man named Cyrian. Cyrian's background and origins are unknown, though he may have been another Time Lord ("Dimensions in Time"). Noel Coward was a close friend and may even have been a travelling companion of the Time Lady known to the Doctor as Iris Wildthyme ("Mad Dogs and Englishmen").