Jimmy is a humanoid abnormal with an abdominal pouch.
He was born and raised in Chicago and lived with his dad. When he was 16 he joined Chicago's King Town Gang where he was made a delivery boy because of his abnormal pouch. He started smuggling guns, drugs, and just about anything he could fit into his pouch for them. The reason why he was so good at smuggling contraband was that items inside of his pouch can't be detected by metal detectors or thermal imaging. In 1989, Jimmy planted the bomb that killed Kate Freelander's father. He finally got out of the gang in 1999, when he was asked to smuggle a Peridax onto a subway train so it could be used as a diversion for a robbery that the King Town Gang was pulling. However, before he got on the train Helen Magnus appeared and warned Jimmy that as soon as he set foot on that train the Peridax he was carrying would release a toxice spray that'd kill everyone on board. That's when Jimmy decided to leave the King Town Gang and start working for the Sanctuary.
He stole a Tunisian fire elemental from a Chicago abnormal mobster named Duke. He brought it to Old City to hand it over to Helen Magnus but is followed by Duke and is unable to make the transfer. He escapes with Kate Freelander, but she is shot in the shoulder. Jimmy manages to get her to an abandoned building and remove the bullet. In their conversations Kate discovered he was the one that planted the bomb that killed her father. She pulls her gun on him but Bigfoot arrived and stopped her. They go to rescue Will Zimmerman and Helen from Duke. Jimmy decides to turn himself over in order to save the team from a shootout but he left the fire elemental in the van and replaced it with a bomb. He entered Duke's car and detonated the bomb, killing them both.
Jimmy's abdominal pouch is a similar concept to the pouch that Jaffa in Stargate posess as a way of protecting and maturing Goa'uld symbiotes.