The Ninth Doctor is the ninth incarnation of the protagonist

Doctor (Doctor Who)

The Doctor is the central character in the long-running BBC television science-fiction series Doctor Who, and has also featured in two cinema feature films, a vast range of spin-off novels, audio dramas and comic strips connected to the series....

 of the long-running BBC

BBC

The British Broadcasting Corporation is a British public service broadcaster. Its headquarters is at Broadcasting House in the City of Westminster, London. It is the largest broadcaster in the world, with about 23,000 staff...

 television science-fiction

Science fiction on television

Science fiction first appeared on a television program during the Golden Age of Science Fiction. Special effects and other production techniques allow creators to present a living visual image of an imaginary world not limited by the constraints of reality; this makes television an excellent medium...

 series Doctor Who

Doctor Who

Doctor Who is a British science fiction television programme produced by the BBC. The programme depicts the adventures of a time-travelling humanoid alien known as the Doctor who explores the universe in a sentient time machine called the TARDIS that flies through time and space, whose exterior...

. He is played by Christopher Eccleston

Christopher Eccleston

Christopher Eccleston is an English stage, film and television actor. His films include Let Him Have It, Shallow Grave, Elizabeth, 28 Days Later, Gone in 60 Seconds, The Others, and G.I. Joe: The Rise of Cobra...

.

Within the series' narrative, the Doctor is a centuries-old alien, a Time Lord

Time Lord

The Time Lords are an ancient extraterrestrial race and civilization of humanoids in the British science fiction television series Doctor Who, of which the series' eponymous protagonist, the Doctor, is a member...

 from the planet Gallifrey

Gallifrey

Gallifrey is a fictional planet in the long-running British science fiction television series Doctor Who and is the homeworld of the Doctor and the Time Lords...

, who travels in time

Time travel in fiction

Time travel is a common theme in science fiction and is depicted in a variety of media. It simply means either going forward in time or backward, to experience the future, or the past.-Literature:...

 in his TARDIS

TARDIS

The TARDISGenerally, TARDIS is written in all upper case letters—this convention was popularised by the Target novelisations of the 1970s...

, frequently with companion

Companion (Doctor Who)

In the long-running BBC television science fiction programme Doctor Who and related works, the term "companion" refers to a character who travels with, and shares the adventures of the Doctor. In most Doctor Who stories, the primary companion acts as both deuteragonist and audience surrogate...

s. When the Doctor is critically injured, he can regenerate

Regeneration (Doctor Who)

Regeneration, in the British science fiction television series Doctor Who, is a biological ability exhibited by Time Lords, a race of fictional humanoids originating on the planet Gallifrey. This process allows a Time Lord who is old or mortally wounded to undergo a transformation into a new...

 his body but in doing so gains a new physical appearance and with it, a distinct new personality.