Doctor Who: 10 Things You Didn't Know About Captain Jack Harkness

10. His Original Name Was Jax

Much like the Doctor, Captain Jack Harkness is a title that he has assumed – it's not his real name. In fact, Russell T Davies' original pitch document for Doctor Who Series 1 made this explicitly clear in the outline for what would become The Empty Child/The Doctor Dances.

Describing the tenth episode of the series, RTD wrote that Captain Jack Harkness was better known as Captain Jax, who was a "futuristic soldier from another world – the captor of the child-creature, here on Earth to track it down." Interestingly, RTD's pitch also states that Rose would feel intimidated by the Doctor and Jax's relationship, as she comes to see Jax as "everything the Doctor’s companion should be."

In the final broadcast version of the story, Steven Moffat gave us a much different yet equally interesting take on this, playing on the differences in approach between Captain Jack – the archetypal matinee idol figure – and the Doctor, the awkward, accidental hero who uses brains rather than brawn. Moffat and RTD also decided to dispose of the Captain Jax name altogether, further heightening the mystery of who Jack really is.

It also avoided confusion with Jax, the Chief Caretaker at Paradise Towers, and would've later avoided clashing with Kahler-Jex, the alien doctor in A Town Called Mercy!