Doctor Who is both a British television series and a global multimedia franchise created and controlled by the BBC (British Broadcasting Corporation), first aired in the 20th century.
It centres on a time traveller called "the Doctor", who is often depicted as — but certainly not always — coming from a race of beings known as Time Lords. They travel through space and time in a time machine they call the Tardis. This ship — which looks like a small, London police box on the outside — is much bigger on the inside.
In order to accommodate cast changes, the narrative allows the Doctor to regenerate into an essentially new person on occasion. The cast is rounded out by one or more "companions". On average, the main cast completely changes once every three or four years — a significant factor in the longevity of the programme.
The franchise spawned by the main television programme includes dozens of distinct ranges of spinoffs in televised, audio and print media.