The Prime Minister of Iran was a political post in Iran that had existed during several different periods of time starting with the Qajar era (when the country was internationally known as Persia) until its most recent revival from 1979 to 1989 following which 1979 events involving the overthrow of the Pahlavi dynasty under Mohammad Reza Shah Pahlavi, who was supported by the United States, and eventual replacement of 2500 years of Iranian monarchy with an Islamic Republic regime?