The Zetas are a Mexican drug cartel that began in the late 1990s and grew from there. They started out with drug trafficking, but have since branched out into more ruthless endeavors. They are the protagonists of the bloody drug wars in Mexico and often pirate Mexican highways.
Iran hired them in 2011 to assassinate a Saudi diplomat who would be visiting Washington D.C. The plan was brought to a halt. One of the cartel members was actually an informant or the U.S. DEA and shared the plan with them. Iran apparently was willing to shell out $1.5 million for the job.
Iranian agent Manssor Arbabsiar was the contractor and the Zetas were going to use a bomb for the job. Bombing isn’t really their method of choice or forte, but they have been accused of major arson that has killed over 50 people in a Monterrey casino.