Claim: The Twelfth Doctor is an alien.

The Twelfth Doctor is an incarnation of the Doctor , the protagonist of the BBC science fiction television programme Doctor Who . He is portrayed by Scottish actor Peter Capaldi . Within the series ' narrative , the Doctor is a time travelling , humanoid alien from a race known as the Time Lords . When the Doctor is critically injured , he can regenerate his body , and in doing so gain a new physical appearance , and with it a distinct new personality ; this plot mechanism has allowed the Doctor to be portrayed by a series of actors over the decades since the programme 's inception in 1963 . Capaldi 's portrayal of the Doctor is a spiky , brusque , contemplative , and pragmatic character who conceals his emotions in the course of making tough and sometimes ruthless decisions .   Capaldi made his first , very brief appearance as the Doctor in the show 's fiftieth anniversary special `` The Day of the Doctor '' -LRB- 2013 -RRB- , as one of the thirteen incarnations of the Doctor who are summoned to save Gallifrey from destruction . Capaldi 's first full appearance as the Doctor was at the end of the 2013 Christmas special `` The Time of the Doctor '' . He is accompanied in the eighth and ninth series by companion Clara Oswald -LRB- Jenna Coleman -RRB- . He also appeared in `` For Tonight We Might Die '' , the first episode of the 2016 spin-off series Class . In the tenth series of Doctor Who , he is accompanied by two new companions : Nardole -LRB- Matt Lucas -RRB- and Bill Potts -LRB- Pearl Mackie -RRB- . On 30 January 2017 , Capaldi announced he would be leaving the programme , with the 2017 Christmas episode being his last .