Ariel Máximo Cantero, widely known as “El Viejo,” is regarded by Argentine authorities and researchers as the historic founder of Los Monos, a criminal organization that emerged in Rosario, Santa Fe. His family became closely associated with the group over several decades, with his sons Claudio “El Pájaro” Cantero and Ariel Máximo “Guille” Cantero later becoming prominent figures in its history.
According to a report by Argentina’s Public Prosecutor’s Office, Cantero assumed the leadership of the group in 2003 following the disappearance of his brother-in-law Juan Carlos Fernández, known as “Mono Grande.” From that point, Los Monos developed into a family-based criminal structure in Rosario, with several members of the Cantero family occupying important positions.
Cantero's criminal record predates the rise of Los Monos in the national spotlight. In 2001, a federal court in Corrientes sentenced him to four years in prison for a drug-trafficking offense involving a marijuana shipment seized in Itatí. Argentine media have identified this as his first major criminal conviction.
His most important later conviction came from the major judicial case against Los Monos. In 2018, Cantero was sentenced to six years in prison for participating in an illicit association. The court case also resulted in lengthy sentences for other members of the organization, including his son “Guille” Cantero and Ramón Machuca, known as “Monchi.”
Cantero was granted conditional release in September 2020 after serving part of that sentence. His return to freedom, however, did not mark the end of his involvement in criminal investigations.
In April 2022, Argentine authorities arrested Cantero again in Rosario. Prosecutors accused him of leading a separate criminal structure allegedly responsible for extortion, attacks and other offenses in neighborhoods in the western and southwestern parts of the city. These accusations were part of a new investigation and should be distinguished from his previous convictions.
The investigation attracted considerable attention because prosecutors alleged that the structure operated under Cantero's leadership. Authorities carried out numerous searches and arrested several suspects in connection with the case. At that stage, the allegations concerned an ongoing judicial investigation rather than final convictions against every person investigated.
His name has continued to appear in Argentine investigations involving Los Monos. In 2025, the Federal Police reported the arrest of a man in Rosario who allegedly maintained communications with intermediaries passing messages from “Guille” and “El Viejo” Cantero. The operation formed part of a broader federal investigation into organized crime in Santa Fe.
The historical significance of “El Viejo” lies largely in his connection to the origins of Los Monos. Argentina's Public Prosecutor's Office describes the group as having developed from a family network in Rosario, with Cantero at the center of its first generation and later relatives assuming increasingly important roles.
His son “Guille” eventually became one of the organization's most prominent figures, while the death of another son, Claudio “El Pájaro” Cantero, in 2013 marked a major turning point in the group's history. The subsequent investigations and trials helped make Los Monos one of the most extensively documented organized-crime cases in Argentina.
As of the latest available reporting, Ariel Máximo “El Viejo” Cantero remains an important historical figure in the story of Los Monos and Rosario's organized-crime investigations. His established convictions should be distinguished from later accusations and investigations in which prosecutors alleged that he continued to exercise influence over criminal structures.
SOURCES
Ministerio Público Fiscal de Argentina — Report on organized crime and Los Monos in Santa Fe
Argentina.gob.ar — Federal Police investigation involving “El Viejo” Cantero
Rosario3 — Three generations of Los Monos
LA NACION — The history of “El Viejo” Cantero and Los Monos
Infobae — The 2022 arrest of “El Viejo” Cantero
