High-Roller is a villain in need of rescue with a faction of Ex-Villain. He can be found on all three missions from the Slot Machine during the "High Roller's Last Gamble" story arc.
High Roller may not have been the most powerful villain in the world before, but now he's fallen on hard times. There may be little honor among theives, but sometimes it's okay to give another guy a break. Hey, one day you might be in the same kind of spot.