This week's Doctor Who Christmas special completes a trilogy of tales in which the Doctor, the 50-year-old BBC TV program's centuries-old Time Lord character, confronts truths about himself. For more than 300 years (his time, not ours), the Eleventh Doctor has kept his greatest secret and its implications regarding his own mortality guarded from everyone, even himself. In "The Name of the Doctor," "The Day of the Doctor," and now "The Time of the Doctor," he comes to face some facts.
In 1966, three years into the program's original run, producers replaced its star, William Hartnell, with actor Patrick Troughton, who did not resemble Hartnell. Within the story, this extraterrestrial character underwent a "renewal" (later known as regeneration), transforming into a new form with the appearance of a different person as a way to heal once the body's previous form was on the verge of death. When the First Doctor's body was "wearing a bit thin," he fell down, turned into the Second Doctor, and arose with altered appearance and personality. Three years later, when Troughton left the part, the Second Doctor became the Third (played by Jon Pertwee) who later become the Fourth (Tom Baker), and so on for 50 years (our time, not his). During the Fourth Doctor's time, a story titled "The Deadly Assassin" established that a Time Lord could regenerate no more than 12 times, which limited each to 13 faces (the original plus 12). In 2010, Matt Smith became the eleventh actor to star as the series lead, making him the Eleventh Doctor. This version of the character has been the first in the modern series (meaning since 2005, when Doctor Who returned from a long-lasting cancellation) to refer to himself by number, in this case "Eleven."
He's been lying to himself.
By thinking of himself as the Eleventh Doctor, the character has let himself ignore the fact that he has used up all 12 regenerations. In "The Name of the Doctor," the last episode of the show's most recent season, he must acknowledge that between his time as the Eighth Doctor (from a TV movie in the middle of the 16 years of cancellation) and when he became the Ninth (the first of the modern series), he'd lived an extra life. His actual ninth form, known within the narrative as the War Doctor, hadn't called himself the Doctor. The so-called Eleventh Doctor tries to avoid even remembering this life, as demonstrated in the episode "Nightmare in Silver" when an enemy called the Cyber-Planner invades the Doctor's mind and finds memories of eleven Doctors. "He's had some cowboys in here," this enemy observes, "10 complete rejigs." When the Doctor's own memory only reveals that he has regenerated 10 times rather than the actual, higher number, maybe that's because he is manipulating his own mind to conceal information from this foe or maybe it's because he has already repressed the truth and hidden it from himself. The Doctor tells the Cyber-Planner, "I could regenerate now," and earlier episodes like "Let's Kill Hitler" indicate that he believes this, that he thinks he's still able to regenerate, but he is wrong.
In "The Name of the Doctor," he admits he'd had an extra self along the way, and then in "The Day of the Doctor," the program's 50th anniversary special, the Tenth and Eleventh Doctors team up with that other self, the War Doctor. (When you're a time traveler, you can come face to face to face with yourself or selves.) The later Doctors have blocked their recollections of what it was like to be the War Doctor, the incarnation that once chose to destroy his homeworld, Gallifrey, in order to save the rest of the universe.
Tenth Doctor: "All those years, burying you in my memory."
Eleventh Doctor: "Pretending you didn't exist. Keeping you a secret, even from myself."
Tenth Doctor: "Pretending you weren't the Doctor when you were the Doctor more than anybody else."
Eleventh Doctor: "You were the Doctor on the day it wasn't possible to get it right."
Even though the Doctor remembers the fact that he destroyed his homeworld Gallifrey, he has avoided remembering the part of himself that made that destructive decision, and his avoidance of the full truth escalates over time. Appalled that his future self has forgotten how many children died on Gallifrey, that the Eleventh Doctor has "moved on," the Tenth Doctor asks, "Where? Where can you be now that you could forget something like that?" Regretting leads to forgetting.
War Doctor (who has not yet reached the point in time where he destroys Gallifrey): "I don't know who you are, either of you. I haven't got the faintest idea."
The Moment (the A.I. that has brought these Doctors together): "They're you. They're what you become if you destroy Gallifrey - the man who regrets and the man who forgets."
After the Tenth and Eleventh Doctors help the War Doctor change his course of action, saving the universe without destroying Gallifrey and therefore removing the Doctor's reason for burying his related memories, the Eleventh Doctor remembers it all. Letting himself remember, however, leads him to realize he has no regenerations left.
When his current traveling companion, Clara, says in "The Time of the Doctor" that he's number eleven, the Doctor replies, "Are we forgetting Captain Grumpy? Hah? I didn't call myself the Doctor during the Time War, but it was still a regeneration."
Clara: "Okay, so you're number twelve."
Eleventh Doctor: "Well, number ten once regenerated and kept the same face. I had vanity issues at the time. Twelve regenerations, Clara. I can't ever do it again. This is where I end up. This face, this version of me."
Fortunately for the Doctor, Gallifreyans reestablish enough contact to bestow upon him a new regeneration cycle. The so-called Eleventh Doctor, who has been the thirteenth in the Doctor's original cycle, becomes the first of the new. At the end of "The Time of the Doctor," he regenerates and begins to change into his next incarnation, a version we call the Twelfth Doctor.
Eleventh Doctor: "We all change. When you think about it, we're all different people all through our lives, and that's okay, that's good. You gotta keep moving so long as you remember all the people that you used to be. I will not forget one line of this, not one day. I swear. I will always remember when the Doctor was me."
The man who forgets has become the man who wants to remember.