Jack Whalen

Jack Whalen (died December 2, 1959), also called Jack O'Hara and "The Enforcer", was a freelance contract killer, who most often worked for the Los Angeles crime family, although he also was associated with Benjamin "Bugsy" Siegel, the Shannon brothers and Mickey Cohen during the 1940s and 1950s.

Whalen's father Fred—who was also a career criminal—had enrolled Jack in military school to give his son a better life. Jack played polo in school and piloted bombers in World War II. After the war, he married into a rich family in Los Angeles; however, by 1955, his own criminal career had begun. He was soon called "The Enforcer" because he was "so tough he didn't need a gun."

He was eventually killed at Rondelli's in Sherman Oaks in the presence of Mickey Cohen and four of his associates, who were charged and later acquitted of his murder.