Which... doesn't explain why Jack is HERE, at least as far as some reasons, but certainly explains the technical bits. Or.. metaphysical bits, as the case may be.
Jack, see, is a mage. Now, when you hear about mages, you may think of Dungeons and Dragons, or Lord of the Rings, or any number of other things, and that's okay, because those guys are mages too. Infinite dimensions means they're also in existence in at least some of them, as well. Different dimensions, though, have different words for things, and in Jack's case, a mage is anyone capable of using magic in combat. Most people can manage little things, where he's from, but being able to keep throwing magic around when people are shooting at you is a Big Deal, especially when they're using magic too! Ditto for fighting monsters(They are USUALLY civilized, but sometimes there's bad apples), or robots, or any sort of thing. Combat in general with magic is tricky!
And, well, as a result, most mages tend to favor ranged attacks. They'll fire bolts or balls or beams or whatever the hell shape of magical energy at their targets, preferably from as far away as possible. Jack, though, is a bit different. You see, in the terms of his world, he's a Knight, more than a mage. He uses magic, but it's geared toward melee offense and personal defense, rather than fields and ranged attacks. That's not to say he can't DO these, but he's... up close. Personal. And VIOLENT. Excessively so, at times, with the help of his Intelligent Device.
Intelligent devices, for those who do not know, are the equivalent of a wizard's staff. They're magical foci, capable of enhancing their user's ability and focusing their will. In the world he's from, they're also designed to provide armor and a weapon/weapons for their user, protecting them from the rigors of combat and allowing them, in theory, to give as good as they get. Staves are still surprisingly common for most mages, but Jack here uses a pair of heavy, mailed gauntlets, getting in close and pounding his enemies into submission if he can.
Jack's look, mind you, depends on what he's doing at the time. Most of the time, he's just a normal-looking guy, maybe 5'8, 5'9ish, with dark hair, kept fairly short(but not super-short), and blue eyes. His skin is fair, and depending on the world, he'll either look a little out of place to VERY out of place, in either jeans and a T-shirt, with sneakers, or something most resembling a school uniform.
Combat, however, requires a different set of clothes. Instead of casualwear, or a uniform, he's actually got armor! Silver plate, form-fitting and set with a large, green gem, is snug against his chest, over an equally form-fitting shirt, where his pants are a simple, snug jeans. His feet sport a pair of stompy boots, made of the same silvery metal as his breastplate, while on his hands he's got a pair of thick gauntlets with somewhat sharp fingers. If one's paying attention, they might notice pulsing green veins of light running through them from the gem in his breastplate, moving along his shirt and into his palms. This whole ensemble is topped off with a headset consisting of a transparent visor over his eyes, as well as an ear-covering metal band, and a deep green duster/trenchcoat type jacket.
Most of the time, though, he's dressed casually, and, assuming humanity is the major sapient species of the world, he fits right in. Except, maybe, for his clothes, but meh, you can't always win.
Personality-wise, he's perpetually cheerful, friendly, and tries to be helpful where he can, at least when it comes to important things. The only thing is, he tends to look over his shoulder a lot, like he's expecting something... Hmn...
