This New York City police Sergeant was often outraged at the bizarre behavior and frequent absences and disappearances of rookie policeman Steve Rogers. Muldoon routinely berated Rogers on more than one occasion.
Muldoon later turned to a life of crime. Taking command of a large group of super-villains and assuming the guise of the hooded "Cowled Commander", Muldoon created a crime-wave of looting in New York City. His schemes were eventually found out and Muldoon and his allies were captured by Captain America and the Falcon. 
Muldoon became fascinated with destroying Captain America. He hired the Manipulator to kill the hero. During the Manipulator's ruse to cause Steve Rogers to lose his mind, Muldoon lost his patience and attempted to shoot Captain America in the back of the head. However, Captain America was only feigning a mental breakdown and quickly subdued Muldoon. Muldoon has apparently been incarcerated since this murder attempt.