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.
UNIT
The Doctor, the main protagonist of "Doctor Who", is a member of UNIT. In "Aliens of London", after reading up about the Doctor during his twelve-month absence, Mickey Smith tells Rose Tyler that the Ninth Doctor knows UNIT because "he's worked for them". In "The Sontaran Stratagem", Colonel Mace tells the Tenth Doctor, "Technically speaking, you're still on staff." In "The Day of the Doctor", the Eleventh Doctor tells Clara Oswald that he works for UNIT and that UNIT is his "job". In "Death in Heaven" (2014), Kate Stewart describes the Twelfth Doctor as "technically" being "on the payroll".