The Doctor is the central character of "Doctor Who". They are an alien, a "Time Lord" from the planet Gallifrey. The Doctor often takes other people with them, who are usually called "companions", "assistants" or "friends" (or, due to a misunderstanding, "partners"). They are most often human. The current companions are Yasmin Khan (as played by Mandip Gill), Ryan Sinclair (Tosin Cole) and Graham O'Brien (Bradley Walsh).