Danny Greene was a notorious underworld figure, union boss, embezzler, Mafia enforcer, and an FBI informant; he 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 Johnston; the gang terrorized the Mason-Dixon Line throughout the 1970s, burglarizing and intimidating victims.

Anibal Mustelier was considered amongst the most dangerous criminals of the Cocaine Cowboy days in Miami; suspected of multiple assassinations and the mastermind behind elaborate bank and jewelry heists.

Omar Portee, aka OG Mack, watches street gangs operate on the West Coast, then brings the knowledge back home to the Bronx, N.Y.; at Rikers Island, Portee creates the United Blood Nation and watches it spread throughout the East Coast.

Juan García Ábrego's cocaine smuggling empire grows to an estimated $10 billion; despite his nickname, The Doll, García Ábrego has a reputation for brutality and is suspected of ordering dozens of killings.

The Aryan Brotherhood of Texas is a white supremacist gang that boasted thousands of members inside and outside of prison throughout Texas and the United States; most of the gang's violence outside of prison is inflicted upon its own members.

David Thai is the leader of the Born to Kill gang, a group of ruthless young men who terrorize Chinatown in New York City; the gang extorts shop owners who are too fearful to turn to police and start a war with rival gangs.

Salvatore "Sammy the Bull" Gravano, the most notorious turncoat in mafia history, pledges loyalty to John Gotti until Gotti himself gets the Bull to change his mind.

Head of the Montreal Mafia, Vito Rizzuto oversees a multi-million dollar international empire reportedly fueled by drug trafficking, money laundering and construction fraud; hard to take down, one act will come back to haunt the Canadian Teflon Don.

Profiling Kaboni Savage, a ruthless drug dealer and murderer; Savage commits murder to protect his interests, even against his rivals' families; Savage's own words ultimately seal his fate.

John Gotti was the last of the classic gangsters in New York City; unlike other mafia chiefs, he loved attention; he ran a multi-million dollar illegal operation that thrived on prostitution, extortion, gambling, theft and drugs.

Richard Kuklinski, one of the most notorious killers in American history, becomes convicted of the murders of four people, but likely killed dozens more; initially a hit man for the Mafia, Kuklinski eventually carries out hits of his own.

The Harvey Hustlers, a notorious gang, dominates the streets of Harvey, La., for three decades; the gang holds a virtual monopoly over the illegal drug trade in the area and is believed to be responsible for at least 45 homicides.

Louis Eppolito and Stephen Caracappa, sworn to protect and serve, instead provide their Mafia cohorts with vital confidential information; the dirty c…