Vincenzo Colosimo[2] (Italian: [vinˈtʃɛntso koˈlɔːzimo]; February 16, 1878 – May 11, 1920), known as James "Big Jim" Colosimo or as "Diamond Jim", was an Italian-American Mafia crime boss who emigrated from Calabria, Italy, in 1895 and built a criminal empire in Chicago based on prostitution, gambling and racketeering.

Al Capone, a close associate of Torrio, has been accused of involvement in Colosimo's murder but was not yet in Chicago at the time.

In 1902, Colosimo married Victoria Moresco, an established Chicago madam[6] and together they began expanding their prostitution business.

Among Colosimo's first brothels was The Victoria (named after his wife), on Archer and Armour Avenue,[7] and The Saratoga, at Dearborn and 22nd Street.

Laurence Bergreen states, "Torrio is [also] described as Colosimo's nephew, but in the absence of any evidence to confirm the relationship, it is more likely their kinship was spiritual rather than familial."

[4] Colosimo's crew grew into a multi-ethnic, hierarchical gang, with Italian, Irish, Polish, and Jewish gangsters.

[8] Contract killer Frankie Yale had allegedly traveled from New York to Chicago and personally killed longtime gang boss Colosimo at the behest of Torrio.

[11] Colosimo was allegedly murdered because he stood in the way of his gang making bootlegging profits, having "gone soft" after his marriage with Winter.