Doctor Who is a science fiction franchise produced by the British Broadcasting Corporation which has existed in various forms since 1963. Central to the franchise is the Doctor Who television series, which originally ran from 1963 to 1989 and was revived in 2005.
The series focuses on the Doctor, a humanoid alien from a culture known as the Time Lords, who travels through space and time in a vehicle called a TARDIS. In these travels, he is usually accompanied by one or more Companions, usually people he meets on his voyages and takes a liking to.
A key plot point in the series is the Doctor's regeneration, an ability triggered when he is near death wherein his body rejuvenates into a new form. Originally used as a convenient way of replacing the lead actor, it has allowed the series to continue for decades as new actors fill the role.