I’ve always wondered about Captain Jack, and what happened to him after Rose brought him “back to life”. I knew that the Doctor had sent him back in time to start over, but i kept wondering if he was going to ever find a way back to DW. However, to my greatest delight, my curiousity about if he was going to return was settled, when Jack finally found DW, and he asked if he’s ever going to die, and DW asked in return, whether he wants to die. i felt really bad for him. Looking back at it, for him to ask that question showed that he was kind of tired of this “never dying” situation. I mean, Captain Jack took the whole “YOLO” business to a whole different level.
It was until the episode of “The Last Time Lords,” that i found out that Jack was actually the Face of Boe. It makes a lot of sense, mainly because the myth about the Face of Boe claims that he was around for billions of years. Thinking of it, Jack could not die, so he became sort of a purposeful-wanderer. Although he could not die, Jack could grow old.
So, my theory is, since Jack could not die, but could age, he grew old with the world, and the billion years he stayed on earth resulted in him becoming just a head in a glass tank, because, seeing as he could grow old, i’m pretty sure his body would not be able to handle the effect of billions of years. I mean it’s the most plausible explanation i have for Jack being the Face of Boe. Oh! and the fact that when he was the first person in the Boeshane Peninsula (Jack’s home colony) to sign up for the Time Agency, they all called him the Face of Boe. While roaming the net, although i cannot remember where i saw it, i read that Jack had stayed with some Headless Monks, and probably that was why he was able to maintain his Head. However, i do not have any explanation on why his head is tentacled.
It was really nice (and shocking!) to know that Jack became The Face of Boe, and that his loyalty to DW went so far, because at the end, it was through the information that The Face of Boe gave DW, that helped the Doctor when he was wondering who The Master really was.