John "Grimjack" Gaunt was the first incarnation of the hero known as Grimjack (from the comic book series of the same name). He is an all around bad ass, and lives by his own set of rules (combine Mel Gibson's character from The Road Warrior with Bruce Willis's character from the Die Hard series, the mix in a little bit of Han Solo, and you get Grimjack).
He lives in Cynosure, a multi-dimension city located at the crossroads of space and time. Cynosure is where all the other dimensions meet. The laws of physics and reality can change quickly in the space of only a few blocks. It is an interesting and dangerous place (it seems to be loosely based on Mos Eisley, with plenty of fantasy and cyberpunk elements tossed in for good measure).
John was born in the poorest part of the city (the area known as "The Pit"), and was convicted of theft at an early age. He was sold to an arena as punishment (where he became a child gladiator), in the arena he met his best friend BlackJacMac (think Wesley Snipes with red sunglasses). Eventually they both escaped the arena. Gaunt made his way to the Pdwyr dimension where he apprenticed as a wizard and fell in love with a young woman named Rhian. He didn't have the control to be a mage, so he left Pdwyr to fight in the "Demon Wars" (a full scale invasion from hell, literally). The entire dimension of Pdwyr was devastated by the wars (as where many others). John went on to work for several law inforcement agencies, but eventually quit the field to go it alone.
He moved back to Cynosure, setting up shop in "The Pit", where he purchased a bar. But the peaceful days didn't last for long. He quickly began working as a detective, mercenary, and general doer of dirty work. He hired Gordon to take over his bar (If I remember correctly he just picked him almost randomly, but that ended up being a good choice), and went out in the world to do the things he had to do.
John is very much a haunted man. He won't let anyone get close to him (not even his undead girlfriend "Spook" or his best friend "BlackJacMac"). He is fiercly loyal, but lets his few past betrayals and failures haunt him. The only thing he is really scared of is himself, gods, demons, and giant robots are not his problem, he is his own problem. John has some mild magical abilities, but he cannot really control them, they do give him some resistance over mental attack though. John also has a very highly developed sixth sense, he can detect lies, unspoken thoughts, and even hidden killer robots. His sense of loyalty and duty causes him to always complete the missions he accepts from people, no matter what the consequences are (many people are in their graves as a direct or indirect result of John's sense of "Duty").
John usually wanders around dressed in a purple outfit that looks something like a pirate. It is the sort of outfit that only a total badass, or an pansy could manage (John is the former, anyone who suspects the latter is usually delt with swiftly). He is always armed to the teeth. Several guns, knives, and a sword are the bare minimum of what this man carries around (usually it is more). Do you remember the scene in Mad Max: Beyond Thunderdome where Max surrendered his weapons, and he had like 30 of them, and then still had a hidden one when he needed it? Well that is how John Gaunt is.
This is where the first issue of the comic book picks up (although much of this backstory appeared in both the Starslayer comic series, and in flashbacks in the normal Grimjack series.
John eventually died (twice), and was reincarnated as James "GrimJack" Twilley, (who eventually could remember both of his lives).