The Doctor (Doctor Who) Time Lords a fixed number of twelve regenerations, meaning that every Time Lord had a total of thirteen incarnations including the original. The plot of "The Time of the Doctor" involves the Doctor receiving a new cycle of regenerations from the Time Lords before his expected demise, triggering the regeneration into the Twelfth Doctor, played by Peter Capaldi. The origins of the programme were explored in the docudrama "An Adventure in Space and Time" as part of the 50th anniversary celebrations of "Doctor Who", which starred David Bradley as William Hartnell. Although Time Lords resemble humans, their physiology differs in
An Adventure in Space and Time Who" in 1993, filmmaker Kevin Davies pitched an idea called "The Legend Begins" to the BBC. "The Legend Begins" would have mixed documentary interviews with those responsible for the creation of "Doctor Who" with a dramatised strand showing the programme's beginnings. Eventually, the dramatisation idea was abandoned in favour of a standard documentary format looking at the entire history of "Doctor Who", which was eventually broadcast on BBC1 as "" in November 1993. Ten years later, for the fortieth anniversary, writer and executive producer Mark Gatiss pitched the idea for the film to BBC Four, unaware of Davies's previous attempt.