Final answer:
The Shah of Iran, Mohammad Reza Pahlavi, came to power in 1941 with the help of Soviet and British forces and later in 1953 with the assistance of the United States' CIA. He was overthrown during the Iranian Revolution in 1979.
Step-by-step explanation:
The Shah of Iran, Mohammad Reza Pahlavi, came to power in two separate occasions. In 1941, during World War II, the Shah was placed in power by Soviet and British forces that invaded Iran. This was due to concerns over German access to Iranian oil. Then, in 1953, with the help of the United States' CIA, the Shah was reinstated after being overthrown by Prime Minister Mossadeq's nationalization of Iran's oil fields.
The Shah remained in power until he was forced to flee in 1979 during the Iranian Revolution. Ayatollah Khomeini returned, and Iran became an Islamic republic. The Shah's policies, supported by the United States, had caused unrest within Iran, and the revolution ultimately led to his downfall.