Julio César Méndez Montenegro was a Guatemalan academic who served as the 34th president of Guatemala from July 1966 to July 1970. Mendez was elected on a platform promising democratic reforms and the curtailment of military power. The only civilian to occupy Guatemala's presidency during the long period of military rule between 1954 and 1986. Mendez had assumed the presidency under a pact in July 1966 that gave the armed forces carte blanche with respect to internal security matters and an effective veto over governmental policy. Nevertheless, his election and swearing in was considered a major turning point for the long military-led Guatemala. He was the first cousin of César Montenegro Paniagua whose kidnapping, torture and murder during the Julio César Méndez presidency is rumored to have been undertaken with presidential sanction.

The president of Guatemala, officially titled President of the Republic of Guatemala, is the head of state and head of government of Guatemala, elected to a single four-year term. The position of President was created in 1839.