Main article: Doctor (Doctor Who)
The ten faces of the Doctor.
(Middle) Tom Baker, Peter Davison, Colin Baker, Sylvester McCoy
(Bottom) Paul McGann, Christopher Eccleston, David TennantThe character of the Doctor was initially shrouded in mystery. All that was known about him in the programme's early days was that he was an eccentric alien traveller of great intelligence who battled injustice while exploring time and space in an unreliable old time machine called the TARDIS, an acronym for Time And Relative Dimension(s) In Space. The TARDIS is much larger on the inside than on the outside and, due to a malfunction of its Chameleon Circuit is stuck in the shape of a 1950s-style British police box.
However, not only did the initially irascible and slightly sinister Doctor quickly mellow into a more compassionate figure, it was eventually revealed that he had been on the run from his own people, the Time Lords of the planet Gallifrey.
As a Time Lord, the Doctor has the ability to regenerate his body when near death. Introduced into the storyline as a way of continuing the series when the writers were faced with the departure of lead actor William Hartnell in 1966, it has continued to be a major element of the series, allowing for the recasting of the lead actor when the need arises.