Danny Greene was a notorious underworld figure. He was a union boss, an embezzler, a Mafia enforcer and an FBI informant. He considered himself a Celtic Warrior, patterned after his beloved Irish lore, and started a war with the Cleveland Mafia, playing with fire until his Irish luck ran out.

The Johnston Gang was a family affair, consisting of Bruce Johnston Sr. and his brothers David and Norman. The gang terrorized the Mason-Dixon Line throughout the 1970s, burglarizing and intimidating victims, and raking in millions of dollars in the process.

The story of Anibal Mustelier, who was one of the most dangerous criminals during the "Cocaine Cowboy" days in Miami.

The story of Omar Portee, aka OG Mack, who reportedly formed the East Coast faction of the Bloods.

The story of Juan Garcia Abrego, the leader of the Gulf Cartel, which was one of the most violent and lucrative drug cartels in Mexican history.

The story of the Aryan Brotherhood of Texas, a violent white supremacist gang that boasted thousands of members inside and outside of prison throughout Texas and the U.S.

David Thai is the leader of the Born to Kill gang, a group that terrorizes New York's Chinatown.

Salvatore "Sammy the Bull" Gravano, the most notorious turncoat in mafia history.

Head of the Montreal Mafia, Vito Rizzuto oversees an empire fueled by drug trafficking.
 

Profiling the ruthless drug dealer and murderer; Savage commits murder to protect his interests.

John Gotti was the last of the classic gangsters; unlike other mafia chiefs, he loved attention.

Mob hit man Richard Kuklinski is the focus.

A notorious New Orleans gang who ruled the streets for three decades are the focus.

Louis Eppolito and Stephen Caracappa give their Mafia cohorts vital confidential information.