Antonio Cardenas Guillen was a Mexican drug lord and co-leader of the criminal organization known as the Gulf Cartel. Antonio was brother of the main drug cartel leader Osiel Cárdenas Guillén, and a business partner of Jorge Eduardo Costilla Sánchez, an ex-policeman.
Born in Matamoros, Tamaulipas, Antonio initially worked as a car washer at a local police station with his brother Osiel. By the late 1980s, he entered the drug trade, and later became the crime boss of Matamoros, where he controlled the city's drug trafficking shipments and all organized crime activities. Few details were known of Antonio's criminal career prior to 1999, when his brother Osiel confronted federal agents at gunpoint with several of his gunmen in Matamoros. In 1998, Antonio avoided arrest after FBI and DEA agents tracked his whereabouts inside a domicile in Houston. Back in Mexico, his brother Osiel was the Gulf Cartel's main leader and had created a paramilitary squad known as Los Zetas, formed by soldiers who left the Mexican military.
When Osiel was arrested in 2003, Antonio and Costilla Sánchez took the lead of the criminal organization, and Los Zetas eventually broke apart from the Gulf Cartel in 2010. However, Antonio was killed in an eight-hour shootout between Gulf Cartel gunmen and soldiers of the Mexican Navy in Matamoros on 5 November 2010. According to the Mexican government, ten people were killed that day in Matamoros, but The Brownsville Herald and The Monitor suggested that at least 47 people were killed by gunfire. One anonymous law enforcement officer, witnesses, and several local newspapers indicated that over 100 were killed in Matamoros.