Grand Unifying Guesses/Captain Jack

Every character who goes by "Captain Jack" is actually the same person.
The list includes:
 * Jack Harkness
 * Whose immortality means this theory is completely plausible.
 * Jack Sparrow
 * Jack Aubrey, from Master and Commander and its sequels.
 * Jack Shaftoe from The Baroque Cycle. Even though he's not a captain.
 * Do they/he intend to get us high tonight, and take us to his/their special island?
 * Well, they do have a tendency to die young shortly after they become good...
 * He also wrote some of the best music in the Dance Dance Revolution series.
 * And the lead from the 1986 comic "Adventures of Captain Jack". Trust me, he is.
 * Harry Kim's uncle
 * Captain Jack of Purgatory
 * Smiling Jack
 * Captain Jack from The Rigabamboo.
 * Deadpool: His real name might be Jack and he was a Captain in the army.