The Doctor is the title character in the long-running BBC science fiction television series Doctor Who, and has also featured in two cinema feature films and one made-for-television film, as well as a vast range of spin-off novels, audio dramas and ... comic strips connected to the series. Within the show, "the Doctor" is the alias assumed by a centuries-old alien who travels through space and time in his TARDIS, frequently with companions.To date, twelve actors have headlined the series as the Doctor, with the transition from actor to actor explained within the narrative of the show through the plot device of "regeneration", a biological function of his race allowing them to completely change their cellular structure and appearance so as to recover from a fatal injury. Several other actors have played the character on stage and film, in audio dramas, and in occasional special episodes of the series. The character's enduring popularity led the Daily Telegraph to dub him "Britain's favourite alien". The incumbent Doctor is the Twelfth Doctor, played by Peter Capaldi, who took over the role from Matt Smith in the 2013 Christmas special "The Time of the Doctor"