The Doctor (Doctor Who)
The Doctor is the title character in the long-running BBC science fiction television programme "Doctor Who". Since the show's inception in 1963, the character has been portrayed by thirteen lead actors. In the programme, "the Doctor" is the alias assumed by a centuries-old alien—a Time Lord from the planet Gallifrey—who travels through space and time in the TARDIS, frequently with companions. The transition to each succeeding actor is explained within the show's narrative through the plot device of "regeneration", a biological function of the Time Lord race that allows a change of cellular structure and appearance with recovery following a potentially fatal injury.
Journey's End (Doctor Who)
One significant feature of this episode is the creation of another Doctor. Unlike the multiple Doctors of stories such as "The Three Doctors", "The Five Doctors" and "The Two Doctors", where his previous incarnations were played by actors or depicted in old footage, this Doctor is identical in appearance to the Tenth Doctor. In the accompanying "Doctor Who Confidential" for this episode, Davies explains "This is so busy and so "mental" and so epic and universal in scale that of course you need two Doctors to solve it." Phil Collinson, Graeme Harper, and David Tennant discuss the use of the double, a musician named Colum Regan who is a very good physical match for Tennant. Collinson explains that while with an unlimited budget they would use Tennant in every shot, "we only have a certain number of effects shots where you can see the two Doctors together, so we have to pick those carefully."