Bill O'Halloran is the father of Rebecca O'Halloran and the head of the O'Halloran family.
Before the Blackout, he was a police officer. His family had a long history in law enforcement.
Some time after the Blackout, he moved his family to Columbus University in Ohio. After Drexel killed his daughter Rebecca, he swore revenge, starting by burning Drexel's poppies. When Miles, Charlie, Aaron, and Nora arrived, Drexel forced Charlie to attempt to kill him. Miles made it to O'Halloran's house in time to save both of their lives.
His guards carried Enfield model 1862 cap-and-ball rifles in violation of the Baltimore Act. How they were able to get away with this is unknown.