Answer
Dulles played key roles in two significant historical events: the 1953 Iranian coup d'état and the 1954 Guatemalan coup d'état. In Iran, he orchestrated the overthrow of the democratically elected Prime Minister Mohammad Mosaddegh, replacing him with the pro-Western Shah Mohammad Reza Pahlavi. In Guatemala, he directed the CIA-backed overthrow of President Jacobo Arbenz Guzmán, installing a military dictatorship.