Excerpts from Books and Wikipedia
"The Americans called it Operation Ajax; Winston Churchill preferred Operation Boot. It's origin lay in 1951, when the shah bowed to pressure and named a new prime minister, Mossadeq, who nationalized Britain's massive Anglo-Iranian Oil Company. A plot was then hatched with the US Central Intelligence Agency, whose agents feared communist infiltration of Iran. Large sums of money bought the complicity of various Iranians, including Zahedi. The CIA referred to the shah as 'a creature of indecision, beset by formless doubts and fear' who 'must be induced to play his role.' So induce him it did. The new regime was provided with $5 million, the Anglo-Iranian Oil Company was returned to British hands and Mossadeq was convicted of treason and imprisoned." [Furtado: 1001 Days]