Question: Who is the former Mexican drug lord and the former leader of the Gulf Cartel and Los Zetas who led the criminal organization?
Context: Efraín Teodoro Torres (died 3 March 2007) was a Mexican suspected drug lord and one of the founders of Los Zetas, a criminal organization formed by former soldiers of the Mexican Armed Forces.  He joined the Mexican Army in mid-1991 but deserted after seven years of service.  In 1998, Torres was recruited by the drug lord Osiel Cárdenas Guillén to join the ranks of the Gulf Cartel, a drug trafficking organization.  The new group formed by ex-commandos came to be known as Los Zetas. Samuel Flores Borrego (a.k.a. Metro 3) (6 August 1972 – 2 September 2011) was a Mexican drug lord and high-ranking lieutenant of the Gulf Cartel.  He was a former state judicial policeman who protected the ex-leader of the Gulf cartel, Osiel Cárdenas Guillén.  Upon his arrest, Flores Borrego became the right-hand man of Jorge Eduardo Costilla Sánchez, the former leader of the criminal organization. Jaime González Durán (a.k.a. "El Hummer") is a former Mexican drug lord who was one of the 31 original founding members and third-in-command of the criminal organization known as Los Zetas.  A former Mexican Army elite soldier of the Grupo Aeromóvil de Fuerzas Especiales (GAFE), he was trained in counter-insurgency and locating and apprehending drug cartel members.  He deserted in the late 1990s and was hired along with 30 other ex-soldiers by the Gulf Cartel leader, Osiel Cárdenas Guillen as his private enforcement army. Gustavo González Castro (born 1 July 1973), commonly referred to by his alias "El Erótico" ("The Erotic One"), is a Mexican drug lord and founding member of Los Zetas, a criminal organization originally formed by ex-commandos from the Mexican Armed Forces.  He joined the Mexican Army as an infantry soldier in 1990, and ascended to the corporal unit five years later.  By 1999, however, González Castro had resigned and began working for the Gulf Cartel and Los Zetas along with several former military men. Sergio Peña Solís (a.k.a. René Solís Carlos, Sergio Peña Mendoza, Arturo Sánchez Fuentes, Rene Carlos Solis), alias “El Concord” and “El Colosio” is a Mexican drug lord and a former leader in the criminal group Los Zetas, then the armed side of the Gulf Cartel.  He was apprehended in Reynosa, Tamaulipas, Mexico, on 14 March 2009. Los Zetas (] , Spanish for "The Zs") is a Mexican criminal syndicate.  Considered by the US government to be "the most technologically advanced, sophisticated, efficient, violent, ruthless, and dangerous cartel operating in Mexico", the organization has expanded beyond the traditional purview of drug trafficking and also runs profitable sex trafficking and gun running rackets.  The origins of Los Zetas date back to the late 1990s when commandos of the Mexican Army deserted their ranks and began working as the enforcement arm of the Gulf Cartel.  In February 2010, Los Zetas broke away from their former employer and formed their own criminal organization. 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.  Originally a mechanic in Matamoros, Tamaulipas, where he was born, he entered the Gulf Cartel by helping Juan García Abrego, the capo at the time; when García Ábrego was arrested in 1996, some infighting erupted within the cartel.  Osiel Cárdenas eventually took control by killing his friend and contender Salvador Gómez, earning Cárdenas the nickname ""El Mata Amigos"" (The Friend-Killer). Rafael Cárdenas Vela (a.k.a. "El Junior") is a former Mexican drug lord and high-ranking lieutenant of the Gulf Cartel.  He is the nephew of Antonio and Osiel Cárdenas Guillén, two men who at one time led the criminal organization. The 2012 Nuevo Laredo massacres were a series of mass murder attacks between the allied Sinaloa Cartel and Gulf Cartel against Los Zetas in the border city of Nuevo Laredo, Tamaulipas, across the U.S.-Mexico border from Laredo, Texas.  The drug-violence in Nuevo Laredo began back in 2003, when the city was controlled by the Gulf Cartel.  Most media reports that write about the Mexican Drug War, however, point to 2006 as the start of the drug war.  That year is a convenient historical marker because that's when Felipe Calderón took office and carried out an aggressive approach against the cartels.  But authors like Ioan Grillo and Sylvia Longmire note that Mexico's drug war actually began at the end of Vicente Fox's administration in 2004, when the first major battle took place in Nuevo Laredo between the Sinaloa Cartel and Los Zetas, who at that time worked as the armed wing of the Gulf Cartel. Óscar Omar Treviño Morales (born January 26, 1974) is a convicted Mexican drug lord and former leader of Los Zetas, a criminal organization.  He was one of Mexico's most-wanted drug lords.  His brother is Miguel Treviño Morales, a former leader of the group.  The authorities believe he was the successor of his brother, who was arrested on July 15, 2013.
Answer: Osiel Cárdenas Guillén