Jesse Porter is a counterintelligence expert, and is accidentally burned by Michael when he was looking for hidden files; but Vaughn had planned that that would happen. Jesse ends up joining Michael's team, and thinks about killing Michael when he learns that Michael burned him. Even though he now holds a grudge against Michael, he stays with the team so he can "do what's right".
Sam: this train is rolling brother; the only question is if you're on board
Jesse: Hell yeah, I'm on board.
Griffin: How did you know my name?
Jesse: It's called research big boy, knowledge is power.