Ruhollah Musavi Khomeini (17 May 1900 – 3 June 1989) was an Iranian cleric , politician, political theorist, and revolutionary who founded the Islamic Republic of Iran and served as its first supreme leader from 1979 until his death in 1989. He was the main leader of the Iranian Revolution , which overthrew Mohammad Reza Pahlavi and transformed Iran into a theocratic Islamic republic .