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.
Doctor Who
Between about 1967 and 1978, large amounts of older material stored in the BBC's various video tape and film libraries were either destroyed, wiped, or suffered from poor storage which led to severe deterioration from broadcast quality. This included many old episodes of "Doctor Who", mostly stories featuring the first two Doctors: William Hartnell and Patrick Troughton. In all, 97 of 253 episodes produced during the first six years of the programme are not held in the BBC's archives (most notably seasons 3, 4, & 5, from which 79 episodes are missing). In 1972, almost all episodes then made were known to exist at the BBC, while by 1978 the practice of wiping tapes and destroying "spare" film copies had been brought to a stop.