The second of two Irish-American "Mad Dogs'" on this list was born in 1939, two years after his namesake was killed. Sullivan's life could have gone very differently if his NYPD detective father hadn't been killed when he was 13. Sullivan turned to crime and contract killing in his teenage years, enlisted in the U.S. Army and ended up in a military prison from which he promptly escaped. He was captured and faked mental illness to get out of the court martial. In fact, escaping prison seemed to be a talent of Sullivan's, as he also broke out of Attica later in life.
Eventually, Sullivan managed to settle down a bit and start a family, but he remained a contract killer. He was implicated in the murders of Mickey Spillane, Tom "The Greek" Kapatos, and the head of the Bonanno Crime family. He's believed to have killed between 20 and 30 people in his career.