Osiel Cárdenas Guillén is a Mexican drug lord and the former leader of the Gulf Cartel and Los Zetas. Originally a mechanic in Matamoros, Tamaulipas, he entered the cartel by killing Juan García Abrego's friend and competitor Salvador Gómez, after the former's arrest in 1996. As confrontations with rival groups heated up, Osiel Cárdenas sought and recruited over 30 deserters from the Grupo Aeromóvil de Fuerzas Especiales to form the cartel's armed wing. Los Zetas served as the hired private mercenary army of the Gulf Cartel.

The Gulf Cartel is a criminal syndicate and drug trafficking organization in Mexico, and perhaps one of the oldest organized crime groups in the country. It is currently based in Matamoros, Tamaulipas, directly across the U.S. border from Brownsville, Texas.