In August 1953 a coup d’état overthrew Iran’s democratically elected Prime Minister Mohammad Mosaddegh in favor of strengthening the monarchical rule of the Shah, Mohammad Reza Pahlavi.
The coup was orchestrated by the United States (Operation Ajax) and the United Kingdom (Operation Boot).
Main Source: 1953 Iranian coup d’état – Wikipedia
Here is a distinctly-Western view of the events.
In 2013 the CIA acknowledged orchestrating the coup