The Tenth Doctor is an incarnation of the Doctor, the protagonist of the BBC science fiction television programme Doctor Who. He is played by Scottish actor David Tennant in three series as well as nine specials. As with previous incarnations of the Doctor, the character has also appeared in other Doctor Who spin-offs. In the programme's narrative, the Doctor is a centuries-old Time Lord alien from the planet Gallifrey who travels in time in his TARDIS, frequently with companions. When the Doctor is critically injured beyond medical repair, he can regenerate his body; in doing so, his physical appearance and personality change, and a new actor assumes the role. Tennant's portrayal of the Doctor is of an outwardly charismatic and charming adventurer whose likeable and easygoing attitude can quickly turn to righteous fury. This incarnation's companions include working class shop assistant Rose Tyler, medical student Martha Jones, and fiery temp worker Donna Noble.