Jack "Legs" Diamond, also known as John Nolan and Gentleman Jack, was an Irish-American gangster in Philadelphia and New York City during the Prohibition era. A bootlegger and close associate of gambler Arnold Rothstein, Diamond survived a number of attempts on his life between 1916 and 1931, causing him to be known as the "clay pigeon of the underworld". In 1930, Diamond's nemesis Dutch Schultz remarked to his own gang, "Ain't there nobody that can shoot this guy so he don't bounce back?"

Arnold Rothstein, nicknamed "The Brain", was an American racketeer, crime boss, businessman, and gambler who became a kingpin of the Jewish Mob in New York City. Rothstein was widely reputed to have organized corruption in professional athletics, including conspiring to fix the 1919 World Series. He was also a mentor of future crime bosses Lucky Luciano, Meyer Lansky, Frank Costello, Bugsy Siegel, and numerous others.