James "Big Jim" Colosimo (1877 – May 11, 1920) (born Giacomo Colosimo), immigrated to Chicago, Illinois from Cosenza , Calabria, Italy in 1895. Beginning as a small time hood, he was noticed by First Ward alderman Michael Kenna and John Coughlin for whom he worked as a precinct captain and later their bagman. These positions provided Colosimo with the political connections which would allow him to advance in his career as a gangster.

In 1902, Colosimo married Victoria Moresco , an established madam, and the two opened a second whore house. Within a few years, Colosimo expanded his business to nearly 200 brothels and had made inroads into gambling and racketeering.

By 1909, he was threatening the Black Hand extortionist group in Chicago and realized he needed help. He brought his nephew, Johnny Torrio to Chicago from Brooklyn, and made him his second in command. The following year, Colosimo opened a self-named restaurant, Colosimo's Cafe, at 2126 South Wabash. In 1919, Torrio and Colosimo opened a brothel at 2222 South Wabash, called the Four Deuces. Torrio brought his old Brooklyn lieutenant, Al Capone to work there as a bartender and bouncer, providing Capone his introduction to Chicago.

When Prohibition went into effect in 1920, Torrio pushed for the gang to enter into bootlegging but Colosimo refused. Having deserted his first wife, Colosimo got married in May, 1920 to Dale Winter . Upon returning to Chicago a week later, Torrio called Colosimo to arrange for Colosimo to meet a shipment at the Café. Upon his arrival, Colosimo was shot in the vestibule. Initial inquiries looked at his bride. Nobody was ever arrested but it is widely believed that Torrio was responsible and arranged for the hit to be carried out by Frankie Yale, a New York gangster.

Colosimo was the first to organize disparate parts of Chicago's crime scene. After his death, his gang was taken over by Torrio and eventually Capone.