Captain Jack Harkness
In naming the character, executive producer and head writer Russell T Davies got inspiration from the Marvel Comics character Agatha Harkness, Jack's original appearances in Doctor Who were thought of with the intention of forming a character arc in which Jack is changed from a coward to a hero, and John Barrowman consciously minded this in his portrayal of the character. Following on that arc, the character's debut episode would leave his morality as ambiguous, publicity materials asking, "Is he a force for good or ill?"