"Big" Louis Costillo (died 1920) was an Italian-American mafioso and the boss of the Chicago Outfit during the Prohibition era. By 1920, he was the last of the old-school mob bosses in Chicago, and he contended both with the Irish hoodlums of the North Side Gang and with his own ambitious lieutenant Johnny Lovo. In 1920, Costillo's bodyguard Tony Camonte shot him dead shortly after a "stag party" in Chicago's First Ward, enabling Lovo to take control of the Outfit.