Born and raised in England, Jack joined the army at the age of 16. He did quite well for himself there, rising to the rank of Sergeant and seeing a lot of action before a medical discharge at the age of 32; by then, secrets had become a way of life.
Once out of the army, he headed for the USA, where he worked as a bounty hunter for a while, mundane and preternatural - though the only preternatural bounties he'd take were for those individual preters who were definite threats to humanity. He became a licensed Vampire Executioner while he was at it, though he didn't see much activity in that line - and then a call came and he went back to the Middle East to help an old friend take care of a problem, with American help.
On his return to the USA, he found out that he'd been given a Federal Marshall's badge, and with his new American contacts, was able to get himself set up a little more to his liking; he took a pin and a map, closed his eyes and decided to move to Chicago. He ended up working for the police as a consultant, and he kept the new badge as quiet as he could.
And then there was another call, a rogue wererat who'd infected several people and needed dealing with. Jack tracked his mark to an isolated spot, only to find that this one was waiting for him. A brief struggled ensued, during which Jack got scratched; the wererat hadn't expected one of the tricks up Jack's sleeves, though, and despite his injuries, Jack won the fight.
Experienced at wilderness survival, Jack stayed in the wilds, bringing down a deer just before full moon, just in case. When he woke up after the full moon to find the carcass stripped, he wasn't too pleased, but accepting that that was life, got to a town, rang the office to let them know, and disappeared back into the woods.
Six months or so later, when he was starting to remember what he did during full moon and get some control over it, he came back to civilisation, to be welcomed with open arms by the Queen of the local Rodere pack and slightly less than open arms by the US Marshall's office. As a Therian, he was no longer in line for a desk job or a promotion - but as a British citizen, he hadn't actually been in line for either anyway. He was allowed to keep his job, and these days is working more closely with the Chicago Police Force.
Just recently, about a year after catching the disease, he was confirmed as an Alpha shapeshifter, his lycanthropic side apparently having settled enough to grow to new power.
Also, Barry Carl as Jack: