Jack is what I'd like to call a "Considerate A-Hole".  He's a cunning fox who likes to troll with people. He's one of those guys whos a jerk, but at the same time he cares about you. VERY egotistical and self-centered. This annoying character is someone that people will love to hate. Even though he isn't the protagonist, he's basically the backbone of the comic. He brings the humor, he moves the plot along, he does just about everything. In the story, he is Xero's roommate and seemingly knows everything that's going on, while Xero knows absolutely nothing. He cares for Xero and the others surprisingly alot, even though he likes to mess around with them.

If he were to sound like any pre-existing character, it would most certainly be Adachi from the Persona 4 series. Try to sound like him as much as possible.

Character Profile: http://www.alexoshrin.com/Jackfighter%20copy.png