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.
The Doctor (Doctor Who)
The BBC novel "The Eight Doctors" was written by respected Doctor Who writer Terrance Dicks, the same author who wrote "The Five Doctors". In it, he tries to reconcile the continuity errors of the 1996 movie, while having the Eighth Doctor meet and interact with each of his previous selves, although the Eighth Doctor visited each incarnation one at a time rather than all eight of them appearing in the same place. Later Eighth Doctor novel "Interference – Book One" sees the Eighth Doctor briefly meeting the Third, although this occasion results in the Doctor unwittingly changing his own history so that the Third Doctor will regenerate ahead of schedule (A change that is later 'reset' in the novel "The Ancestor Cell" thanks to the TARDIS taking action to preserve the original history). In the Past Doctor Adventures, the novel "Heart of TARDIS" features the Second and Fourth Doctors dealing with two different ends of the same crisis, with the Second Doctor trapped in a dimensional anomaly created by a government experiment and the Fourth recruited to stop the experiment destroying the world, but although they are at one point both in the Second Doctor's TARDIS, the Fourth Doctor and his companion hide on the opposite side of the console from his past self and the Second is never aware of his future self. In "The Colony of Lies", the Second Doctor briefly interacts with the Seventh Doctor in a VR simulation, but it is unspecified if this is the actual Seventh Doctor or just a VR program he left to advise his past self. In "Wolfsbane", like in "Heart of TARDIS", the Fourth and Eighth Doctors deal with separate ends of the same crisis, the Eighth stopping the threat in November 1936 while the Fourth ties up loose ends in December of the same year, but the two incarnations never meet directly, and due to the Eighth Doctor's current amnesia none of the other characters realize that the two Doctors are the same person.