• Leader of the Gulf Cartel Antonio Ezequiel Cárdenas Guillén, 1962

Cárdenas is believed to have begun his drug trafficking career during the late 1980s, rising through the ranks of the Gulf Cartel and becoming its leader after the arrest of his brother Osiel Cárdenas Guillén on March 14, 2003. Antonio, along with other Gulf Cartel associates, was responsible for multi - ton shipments of marijuana and cocaine from Mexico to the United States.

The Gulf Cartel, originally founded in Mexico the 1930s to smuggle whiskey and other illicit commodities into the United States, expanded significantly by the 1970s under Juan García Abrego, who became the first drug trafficker to be placed on the FBI's Ten Most Wanted List. Following his 1996 arrest by Mexican authorities and subsequent deportation to the United States, Oscar Malherbe De León took control of the cartel until his arrest a short time later. He was replaced by Osiel Cárdenas Guillén, who was arrested in 2003, and extradited to the United States in 2007. The Gulf Cartel currently controls most of the cocaine and marijuana trafficking through the Matamoros, Tamaulipas corridor to the United States. The Attorney General of Mexico suspects that his partner Jorge Eduardo Costilla had taken full control of the Gulf Cartel.

Antonio Cárdenas Guillén became the co-leader of the Gulf Cartel, along with Jorge Eduardo Costilla Sánchez, alias El Coss, after the extradition of Osiel Cárdenas Guillén. El Coss was often viewed as the "strongest leader" of the two, but collaborated with Tony Tormenta, who acted as representative of his brother in jail. However, Ezekiel died in an eight hour shooting with the Mexican government forces on November 5, 2010 in the border city of Matamoros, Tamaulipas. Government sources claimed that this operation — where more than 660 marines, 17 vehicles, and 3 helicopters participated — left 8 dead: three marines, one soldier, and four gunmen, including Antonio Cárdenas Guillén. Other sources mention that one news reporter was also killed in the crossfire. This military led operation was a result of a work of more than six months of intelligence work and some operational actions. Milenio Television mentioned that the Mexican authorities had tried to apprehend Cárdenas Guillén twice before this incident, but that his personal gunmen had distracted the Mexican forces and allowed him to be escorted in his armored vehicle.

The confrontations started around 10:00AM, and extended to 06:00PM, around the time Cárdenas Guillén was killed. The intense shootings provoked the temporary closure of three international bridges in Matamoros, along with the University of Texas at Brownsville, just across the border. Public transportation and school classes in Matamoros were canceled, along with the suspension of activities throughout the municipality, since the cartel members hijacked the units of public transport and made dozens of roadblocks to prevent the mobilization of the soldiers, marines and federal police forces. The street confrontations generated a wave of panic among the population and caused the publication and broadcast of messages through social networks like Twitter and Facebook, reporting the clashes between authorities and the cartel members. When the Mexican authorities reached the spot where Tony Tormenta was present, the gunmen received the soldiers and cops with grenades and high caliber shots. Reports mention that Antonio Ezekiel Cárdenas Guillén was being protected by the Los Escorpiones, or The Scorpions, the alleged armed wing of the Gulf Cartel and the personal army of Ezekiel, who were serving as snipers and bodyguards for him. La Jornada newspaper mentioned that over 80 SUVs packed with gunmen fought to protect Cárdenas Guillén, and over 300 grenades were used in the shootout that day. And even after the drug lord was killed, the roadblocks continued throughout the rest of the day.

The Guardian newspaper mentioned that in a Youtube video, a convoy of SUV's filled with gunmen and pickups packed with marines were seen in a chase through the streets of Matamoros, Tamaulipas. And although there wasn't any visible confrontation between the two, the intensity of the situation was clear through the background noises of grenades explosions and automatic gunfire. A news video from Televisa, also on Youtube, shows images from the confrontations of that day. Moreover, several bystanders also recorded the shootouts.

Nevertheless, according to the newspapers The Brownsville Herald and The Monitor from across the border in Brownsville, Texas, and McAllen, Texas, around 50 people were killed in the gunfights. Although not confirmed, KVEO-TV, several online sources and witnesses, along with one law enforcement officer who preferred to keep his name anonymous, mentioned that more than 100 people died that day in Matamoros. The death of Tony Tormenta also caused a spiral of violence in Reynosa, Tamaulipas, a number of days after he was killed. Moreover, his death also generated a turf war with Los Zetas in the city of Ciudad Mier, Tamaulipas, resulting in the exodus of more than 95% of its population. Banners written by Los Zetas, the Gulf Cartel's former armed wing, appeared all across Mexico, celebrating the death of Cárdenas Guillén. The United States president, Barack Obama, called the president of Mexico, Felipe Calderón, congratulating him and the Mexican forces for the operation in Matamoros, and reiterated his support for the efforts against organized crime.

After this incident, there was a huge division of opinions over the fate of the Gulf Cartel. Some experts believed that the death of Ezekiel would be dreadful for the Gulf Cartel, and that Los Zetas would overthrow them and eventually take control of Tamaulipas. Others explained how his death allowed Costilla Sánchez to take full direction of the cartel, and that that would tighten relations with Colombia and straighten the Gulf Cartel’s path, something quite difficult with Ezekiel as co-leader.

Los Escorpiones, also called Grupo Escorpios, (The Scorpions), was believed to be the mercenary group that protected Antonio Ezekiel Cárdenas Guillén, the former leader of the organization. According to reports by the Mexican government, Los Escorpiones was created by Tony Tormenta and is composed of over 60 civilians, former police officers, and ex-military officials. According to El Universal, there are several music videos on Youtube that exalt the power of this armed group through narcocorridos. After the rupture between the Gulf Cartel and Los Zetas (which until then had served as the cartel's armed wing), Los Escorpiones became the armed wing of the entire Gulf organization. The first mention of Los Escorpiones on the media was in 2008, when El Universal wrote an article about some "protected witnesses" from the Gulf Cartel who denounced the alliance between the Beltrán - Leyva Cartel and Los Zetas to the Mexican authorities, and that the Gulf Cartel had created Los Escorpiones to stop and balance the growing hegemony of Los Zetas.

However, his brother Osiel Cárdenas Guillén disapproved the existence of this mercenary group, since he had created Los Zetas, the parallel version of Los Escorpiones, and they had turned against the organization. El Universal reported that Mexican authorities identified the gunmen that where engaging in confrontations with the troops in Matamoros, Tamaulipas, as members of the Los Escorpiones group. Along with Antonio Cárdenas Guillén, the following members of Los Escorpiones were killed: Sergio Antonio Fuentes, alias El Tyson or Escorpión 1; Raúl Marmolejo Gómez, alias Escorpión 18; Hugo Lira, alias Escorpión 26; and Refugio Adalberto Vargas Cortés, alias Escorpión 42. The arrests of Marco Antonio Cortez Rodríguez alias Escorpión 37 and of Josué González Rodríguez alias Escorpión 43 — the two who were hospitalized after the shootout of 5 November 2010 — allowed for the Mexican forces to understand the structure of Los Escorpiones.

Cárdenas was one of the eleven 'Most Wanted' Mexican fugitives sought by the U.S. Drug Enforcement Administration (DEA). He was charged in a 2008 federal indictment in the District of Columbia, and the U.S. Department of State was offering a reward of up to $5 million USD for information leading to his arrest, while the Attorney General of Mexico was offering a 30 million pesos bounty (about $2.5 million USD).