Mario Cárdenas Guillén is the brother of the Mexican drug lord who was the former leader of what group?
Mario Cárdenas Guillén:  He is the brother of Osiel Cárdenas Guillén and Antonio Cárdenas Guillén. Osiel Cárdenas Guillén: Osiel Cárdenas Guillén (born May 18, 1967) is a former Mexican drug lord and the former leader of the Gulf Cartel (Spanish: "Cártel del Golfo" ) and Los Zetas.
Gulf Cartel