Question: Mario Cárdenas Guillén is the brother of the Mexican drug lord who was the former leader of what group?
Sentence (from "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.
Relevant evidence: Yes