Julio César Méndez Montenegro (November 23, 1915 – April 30, 1996) was the Revolutionary Party President of Guatemala from July 1, 1966 to July 1, 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, Méndez was not allowed to act independently of the military and was widely considered to be a military puppet; 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.
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.