Adolfo López Mateos was a Mexican politician who became a member of the Institutional Revolutionary Party, after earlier opposing its precursor in 1929. He was elected President of Mexico, serving from 1958 to 1964.
As president, he nationalized electric companies, created the National Commission for Free Textbooks, settled the Chamizal dispute, and opened important museums such as the Museum of Natural History and the National Museum of Anthropology in Mexico City. Declaring his political philosophy to be "left within the Constitution", López Mateos was the first self-declared left-wing politician to hold the presidency since Lázaro Cárdenas. López Mateos was well known for being very popular among the Mexican people; alongside Cárdenas and Adolfo Ruiz Cortines, he is usually considered one of the most popular Mexican presidents of the 20th century, despite acts of repression during his administration such as the arrest of union leaders Demetrio Vallejo and Valentín Campa, and the murder of peasant leader Rubén Jaramillo and his family by the Mexican army.