John Hurt is an Oscar-nominated actor most famous for his role as Kane in the 1979 movie Alien, in particular the (in)famous "chest-bursting" scene. This movie and the actor John Hurt apparently exist in the Doctor Who universe, as Toshiko Sato references the scene in "Greeks Bearing Gifts", specifically mentioning Hurt by name. Most recently, he spent five seasons performing the voice of the Dragon in Doctor Who's sister series at BBC Cymru, Merlin, and he also had a recurring role as Mr. Ollivander in the Harry Potter films.
Hurt made his first appearance on Doctor Who in the 2013 episode "The Name of the Doctor", in which he was revealed as an as-yet-unexplained incarnation of the Doctor. The Eleventh Doctor and Clara Oswald encounter him when the Doctor enters his own timestream to save her. Eleven said that he chose the name "the Doctor" for himself as a promise, and that this incarnation broke that promise. This forgotten incarnation, the Doctor's secret, defended his actions saying that he did them for "peace and sanity". The Eleventh Doctor didn't dispute this, but did suggest that because of what he did he could not properly call himself "the Doctor". Despite this, Hurt is directly credited on screen - twice, in the final scene and during the closing credits - as the Doctor. We do not as yet know what ordinal number (if any) to assign this incarnation. Hurt has been confirmed as reprising the role in the upcoming 50th anniversary special.