The Outfit rose to power in the 1920s, under the control of Johnny Torrio and Al Capone and the period was marked by bloody gang wars for distribution of illegal alcohol during Prohibition. Since then, the Outfit has been involved in a wide range of criminal activities, including loansharking, gambling, prostitution, extortion, political corruption, and murder. Following Capone's conviction for income tax evasion (in 1931), the Outfit was run by Paul Ricca and Tony Accardo for more than 50 years. Accardo took over as boss sometime in the 1940s and was one of the longest sitting bosses of all time right up until his death in the early 1990s.
The Outfit did not have a monopoly on organized crime in Chicago, but they were by far the most powerful, violent and largest criminal organization in the Midwest. The Outfit's influence, at its peak, stretched as far away as California and Florida. Higher law enforcement attention and general attrition led to the Outfit's gradual decline since the late 20th century. As of 1997, the Chicago Outfit was believed to be led by John DiFronzo.
The early years of organized crime in Chicago, in the late 19th and early 20th centuries, were marked by the division of various street gangs controlling the South Side and North Side, as well as the Black Hand organizations of Little Italy.
Big Jim Colosimo centralized control in the early 20th century. Colosimo was born in Calabria, Italy, in 1877, emigrating to Chicago in 1895 where he established himself as a criminal. By 1909, he was successful enough that he was encroaching on the criminal activity of the Black Hand organization.
His expanding organization required the procurement of extra muscle. This came in the form of Colosimo's nephew Johnny Torrio from New York. In 1919, Torrio brought in Al Capone, thus providing Capone's entrance to Chicago. In time, Colosimo and Torrio had a falling out over Torrio's insistence that they expand into rum-running, which Colosimo staunchly opposed. In 1920, Colosimo was killed on Torrio's order. Torrio reportedly brought in New York colleague Frankie Yale to murder Colosimo. Al Capone has also been suspected as Colosimo's assassin.