Member of Mythos, dying for action.
Jack always feels "happy". Law Co wanted him to always feel "happy". They did experiments on him to make him feel "happy", and he always did. But as the years go by, Jack no longer feels "happy" unless he inflicts it upon himself via the way Law Co did. When he's not "happy" he is extremely depressed and irritable. No one wants to talk to him, and he sulks and thinks about suicide. When Jack is "happy", he is charismatic, a jokester, and your everyday dude. He also has a tendency to care about everyone that he comes in contact with whether he is "happy" or normal.
Jack has the ability to manipulate electricity and (somewhat) light. If there is any kind of spark anywhere, he could amplify it and kill someone with it. However, the smaller the original amount of electricity, the more dangerous it is for Jack. He sometimes carries around some batteries and some sort of toy or appliance (specifically a BINGO game), that way he always is able to use his powers if he needs to. Near the end of his Law Co experiments, he was briefly able to move light. He could use this to make himself or something else invisible, or to blind someone. But he is only able to do this for a few seconds, and it really isn't that useful.
Jack was from a family that hurt many people. His father owned a nuclear company, which constantly laid off people, leaving them homeless. He always thought losing Jack was a punishment, and it was. Law Co taught Jack to hate his father. Ever since he was released, he has been working for MYTHOS, doing various odd jobs.