He was angry at the O'Brien Pack for letting some lone Omega werewolf slip past them and manage to kill his father. Intellectually, Jack knew it wasn't their fault; the Omega had instinctively avoided them, and it was clearly quite dangerous if it got the drop on Dave Colton, but Jack couldn't help being angry about it…weren't the O'Briens supposed to be the guardians of Signal Lakes? Protecting its residents from paranormal threats, like violently insane Omega werewolves? Shouldn't they be able to guard against their own kind better than any other paranormal problem!?
But then they went and got themselves killed in their own home, right before Christmas, a month after Jack's dad was slain. Part of Jack wanted to be bitter and say they clearly sucked as guardians, but he knew his dad would have told him that wasn't fair. They had protected this city from itself, as the tip of the Bermuda Triangle, for well over a century; it wasn't their fault they were assassinated over the holidays. Some group of rogue Hunters ringed their house with mountain ash and burned them alive inside of it, and now Jack and his mom had to pick up the pieces.
Jack strapped on his forearm-sheath slingshot and set off into the murky forest of the swamp, armed with iron pellets. A Dark Fae something was kidnapping children from the nearby park, and that was something Jack was not going to allow.
He was going to find that Fae, and show it exactly how he felt about things.
Hunters are otherwise ordinary human beings who have chosen to defend humanity against the paranormal, who Hunt down the creatures that prey on people, and kill them. It's a mostly thankless job, and a highly dangerous one, but Hunters have some advantages. They have both training and knowledge most of the rest of the world does not, and they know how to put those things to use with the appropriate equipment to get the job done.
In the context of the game, Hunters are almost the same as ordinary humans, but instead of being lucky, they are skilled. Hunters have access to Skills and abilities that other Creature Types do not, including psychics and normal humans. A Hunter character may also have a fair number of their Character Creation Points spent on Capabilities, making them stronger, tougher, faster, or whatever other improvements their Player feels will make the character into a better Hunter.