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)
In the following episode, "Deep Breath" (2014), the Twelfth Doctor states that he is over 2,000 years old. However, writer Steven Moffat has said, "He's lying. How could he know, unless he's marking it on a wall? He could be 8,000 years old, he could be a million. He has no clue. The calendar will give him no clues." In the episode "The Girl Who Died" the Doctor is shown to possess a 2000 Year Diary. Moffat later said that he believes the Doctor remembers all 4.5 billion years he spent dying and recreating himself in "Heaven Sent" (2015), and that the confession dial extracts the Doctor's memories of each iteration, feeding them back to him as a means of torture. In a subsequent interview with "SFX", Moffat confirmed, "Technically he's four and a half billion years old."