Duke

 is a diukon that had risen to a position of power in the Chicago Mob. He did this courtesy of a rage controller that enabled him to overcome his natural tenancies for violence and rage.

He tracked Jimmy to Old City to obtain the Tunisian fire elemental he had stolen. He kidnapped Dr. Will Zimmerman and forced Dr. Helen Magnus to give up Jimmy in exchange. Jimmy turned himself over in order to save Will and Helen but left the Fire Elemental in the van and replace it with a bomb. He entered Duke's car and detonated the bomb, killing them both.