major American gangster, the top syndicate boss in Chicago from 1957 to 1966, who was noted for his friendships with show-business personalities and for his ruthlessness.

Born and reared in Chicago's “Little Italy” on the near southwest side, Giancana began working for Al Capone in the 1920s and, by 1966, had been arrested some 70 times and served five years in prison for burglary and four years for operating an illegal still. In 1965–66 he spent a year in jail for contempt of a federal grand jury (1965) that had granted him immunity in return for testimony, an offer that he had rebuffed. After release from prison he disappeared into Mexico, Argentina, and other Latin-American countries to avoid further U.S. government inquiry. In July 1974, however, he was seized by police in Mexico City and shipped back to Chicago. One year later he was bullet-riddled in his home in Oak Park, Ill., by unknown assailants. He had been scheduled to appear before the U.S. Senate Intelligence Committee to discuss his alleged involvement in a Central Intelligence Agency plot to assassinate Fidel Castro in the early 1960s.