James "Whitey" Bulger reigned supreme in Boston's underworld for more than 20 years. His rise to power, as part of South Boston's Irish-American Winter Hill gang, was due in part to a remarkable relationship with the FBI.

Murder, Inc. is the name for a ruthless gang that carried out mob hits during the 1930s.

He was one of the most successful and notorious members of the Italian American Mafia. During Tommy's tenure as underboss and boss of what would come to be known as the Lucchese crime family.

"Big Paul" Castellano served as boss of the Gambino crime family—the largest in New York during the 1970s and '80s.

A volatile temper and a legendary flair for fashion helped John Gotti rise to the top of the Gambino crime family—and become one of the most well-known figures in Mafia history.

In New Orleans, Carlos Marcello joined the mob at 26 and quickly climbed the ranks, aided by success in illegal gambling ventures and a talent for making effective payoffs to public officials.