They’ll extort you, force you to sell and smuggle their drugs — and, if you resist, leave you for dead.
Violent gangs have long muscled their power inside U.S. prisons and pose a constant threat to the safety of everyone behind bars, both inmates and staff.
Here is a look at the most notorious prison gangs:
The Aryan Brotherhood is one of the most ruthless prison gangs in the U.S.
Also known as The Brand, the Aryan Brotherhood started in California's San Quentin State Prison in 1964.
The AB has grown from a gang with racist ideology to a moneymaking organization that resembles a traditional organized crime family, according to the FBI.
The gang runs protection rackets, extortion, drug trafficking and contraband smuggling, as well as assaults for hire inside and outside prisons.
The AB exists in dozens of states but is strongest in California and Arizona.
In the federal prison system, the FBI alleges its members make up less than one-tenth of 1% of inmates but are responsible for 18% of all prison murders.
Members are identifiable by their tattoos, which include Nazi and Viking imagery and, typically, a prominently displayed shamrock.
The Mexican Mafia control thousands of Latino street gang members.
The Mexican Mafia, also known as "Le Eme," began in the California prison system in the 1950s.
The gang is active in state prison systems throughout the U.S. and in the federal prison system.
They specialize in extortion, drug dealing, contraband smuggling, assaults and murder-for-hire, according to the FBI.
Eme members, which are estimated to number around 200, control thousands of Hispanic inmates and street gang members, according to the Department of Justice.
They are typically identified by a black hand print tattoo or the number 13 — signifying the letter M, the 13th in the alphabet.
The Nazi Low Riders membership grew rapidly in the 1990s.
The Nazi Low Riders formed in the California Youth Authority in the late 1970s.
It emerged as a force in California's prison system in the 1990s when authorities cracked down on the Aryan Brotherhood.
NLR members have been linked to murders, home-invasion robberies, witness intimidation, drug dealing and assaults on police officers, according to the U.S. Department of Justice.
The NLR, with its white-supremacist philosophy, has recruited from the ranks of skinheads.
According to the Arizona Department of Corrections, the NLR has established a significant presence in the Arizona state prison system and is considered a monitored Security Threat Group.
Black Guerilla Family
The Black Guerilla Family was implicated in a massive corruption probe of the Baltimore City Jail last year.
Founded in the California prison system in the 1960s, the BGF is highly organized with a rigid leadership structure, according to the Department of Justice.
The BGF has a black power ideology, but will work with other racial groups, like the Nuestra Familia, on criminal matters, including drug trafficking, prostitution, and assaults.
The BGF is active in the federal prison system as well as the California and Maryland state prison systems, according to the FBI. BGF members were implicated in a massive corruption case in the Baltimore City Jail in 2014, which included the facility's BGF leader fathering at least four children with corrections officers.
Authorities prosecuted the leadership of Nuestra Famlia in a 2001 case.
The Nuestra Familia originated in the California prison system in response to perceived victimization of northern California Mexican inmates by the southern-dominated Mexican Mafia.
The gang makes significant income from standard prison rackets like extortion, drug dealing, assaults, and contraband smuggling.
In addition to a strong presence in the California state prison system, NF members are reported in the Colorado, Arizona, Texas and New Mexico prison systems, according to the FBI.
The NF has a loose alliance with the Black Guerilla Family, based on the two gangs mutual rivalries with the Aryan Brotherhood and Mexican Mafia.