Scariest fact: They're like Navy SEALS, but completely illegal.
Murder weapons: Rocket launchers and semiautomatic handguns.
Los Zetas were originally members of an elite force in the Mexican army, then one day they decided to go AWOL and become gang lords. (Imagine how nuts it would be if a handful of Navy SEALS decided to join the Crips.) Los Zetas was founded in the 1990s when skilled members of the Mexican army went rogue to operate under the Gulf Cartel. In 2000, they broke away from the Gulf Cartel to form their own independent gang. The United States government recognizes Los Zetas as "the most technologically advanced, sophisticated and dangerous cartel operating in Mexico." The gang deals in assassinations, extortion, kidnapping, oil, and the drug trade. They are incredibly violent. In August 2011, they set fire to a casino in Monterrey, Nuevo León in Mexico killing 52 innocent people.