10 Doctor Who Fan Theories That Will Blow Your Mind
2. Captain Jack Was Beheaded By The Headless Monks
Captain Jack Harkness had quite the life, living for millions of years and eventually turning into the Face of Boe - an enormous, humanoid head (this is never explicitly confirmed in the show, but is commonly regarded as canon). But how did he go from being a normal human, to just a head? Is that what happens when humans live to such a grand age? Or is there another explanation?
Of course there is! Captain Jack was originally slated to appear in A Good Man Goes To War, but actor John Barrowman was unable to, due to scheduling conflicts. That episode's villains are the Headless Monks, robed religious figures who wield laser swords and like to cut off people's heads. Lovely. Since Jack was supposed to be a part of this story, it's speculated that the Monks would have taken his head, which would have turned into the Face of Boe, millions of years down the line.
A Good Man Goes To War writer Steven Moffat was the one who first introduced Jack back in Series 1 of the modern era, so it makes sense that he'd try to further flesh out the character's story here.