The question was first asked all the way back in the '80s. Colin Baker was playing the Sixth Doctor on Doctor Who back then. At the end of his run, there was a season-long story arc about the Time Lords putting him on trial. They were hoping they'd get to execute him, since he'd seen them do some terrible shit. The prosecutor was a future version of the Doctor. But he wasn't called the Doctor. He was called the Valeyard. And he was evil. He wanted to steal all the Doctor's future regenerations for himself.That's him in the photo. The Master explained who he was: "an amalgamation of the darker side of the Doctor... [his] penultimate reincarnation... Somewhere between [his] twelfth and final regeneration." And by final regeneration, he meant the 13th. Time Lords are only supposed to get 13 incarnations. That was mentioned all the way back in 1976.
Since then, people have been wondering what would happen when the show finally did get to that point in the Doctor's timeline. Would the Valeyard appear? Would the Thirteenth Doctor really be the final Doctor? It was never an immediate concern, though. The Thirteenth Doctor was always a ways away.
In recent years, it seemed as if the show might just sidestep the question altogether. In fact, when Matt Smith made a guest appearance as the Eleventh Doctor on the spin-off series The Sarah Jane Adventures, he was asked how many regenerations a Time Lord gets. "507," he said. Some people took that to mean the number had changed. Others dismissed it as a joke. Meanwhile, the series continued on without any further mention of the regeneration limit. Or of the Valeyard.
But that all changed in this year's season finale. For one thing, the question is now suddenly a pressing one. At the very end of the episode, we learned that [spoiler] Matt Smith's Doctor may not, in fact, be the Eleventh Doctor at all. John Hurt fits in there somewhere. And even if he isn't technically known as "The Doctor", it seems likely that he does count as an incarnation. Which makes Matt Smith the 12th. And the next Doctor — Peter Capaldi — the 13th.
So what does that mean? Will Peter Capaldi be the evil Valeyard and, like John Hurt, not a "true" Doctor? Will the Valeyard appear somehow between the Matt Smith and Peter Capaldi Doctors so that he can head off into the past to prosecute Colin Baker's Doctor? Will Peter Capaldi be the final incarnation? Or will the show find a way around the regeneration limit? Did River Song give him extra lives when she healed him? Did the limit cease to apply when David Tennat's Doctor banished Rassilon, the founder of the Time Lords, back into the time-locked Time War? What's going to happen when we get to the 507th Doctor?
Who the hell knows? But the Valeyard did get name-dropped in the season finale. The Great Intelligence mentions him when he's listing all the names the Doctor is known by over the years. So, at the very least, it seems they aren't completely ignoring that storyline. There might still be some Valeyard to come.
Read our recaps of recent Doctor Who episodes here. Learn about the Doctor's very first secret from 1963 here.