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 with his emotional attachment to the character; with little choice, he reluctantly accepts the situation. He breaks into tears as he informs his wife Heather (Lesley Manville) of the news, admitting that he doesn't want to leave the role. Before his final scene, Hartnell shares a brief exchange with his successor, Patrick Troughton (Reece Shearsmith). As the cameras are about to record, Hartnell looks across the main console and sees Matt Smith, who will play the same role nearly 50 years later. Smith silently acknowledges Hartnell's legacy before disappearing as Hartnell begins the scene. For the thirtieth anniversary of "Doctor