Ruhollah Khomeini (UK: khom-AY-nee, US: khohm-; Persian: روح‌الله خمینی, romanized: Rūḥallāh Khumaynī, pronounced [ɾuːholˈlɒːhe xomejˈniː] (listen); born Ruhollah Mostafavi Musavi; 17 May 1900 – 3 June 1989), also known as Ayatollah Khomeini, was an Iranian political and religious leader who served as the first supreme leader of Iran from 1979 until his death in 1989. He was the founder of the Islamic Republic of Iran and the leader of the 1979 Iranian Revolution, which saw the overthrow of Shah Mohammad Reza Pahlavi and the end of the Persian monarchy. Following the revolution, Khomeini became the country's first supreme leader, a position created in the constitution of the Islamic Republic as the highest-ranking political and religious authority of the nation, which he held until his death. Most of his period in power was taken up by the Iran–Iraq War of 1980–1988. He was succeeded by Ali Khamenei on 4 June 1989.

Khomeini was born in Khomeyn, in what is now Iran's Markazi province. His father was murdered in 1903 when Khomeini was two years old. He began studying the Quran and Arabic from a young age and was assisted in his religious studies by his relatives, including his mother's cousin and older brother.

Khomeini was a high ranking cleric in Twelver Shi'ism, an ayatollah, a marja' ("source of emulation"), a Mujtahid or faqīh (an expert in Sharia), and author of more than 40 books. He spent more than 15 years in exile for his opposition to the last shah. In 1970, in his writing and preaching, he began expanding on the theory of Velâyat-e Faqih, the "Guardianship of the Islamic Jurist (clerical authority)", to include theocratic political rule by Islamic jurists. This principle, though not known to the wider public before the revolution, was appended to the new Iranian constitution after the revolution. He was Time magazine's Man of the Year in 1979 for his international influence, and Khomeini has been described as the "virtual face of Shia Islam in Western popular culture", where he was known for his support of the hostage takers during the Iran hostage crisis, his fatwa calling for the murder of British Indian novelist Salman Rushdie, and for referring to the United States as the "Great Satan" and the Soviet Union as the "Lesser Satan". Khomeini has been criticized for these acts and for human rights violations of Iranians (including his ordering of attacks against demonstrators, execution of thousands of political prisoners, war criminals and prisoners of the Iran–Iraq War).

Khomeini has also been lauded as politically asute, a "charismatic leader of immense popularity", a "champion of Islamic revival" by Shia scholars, and a major innovator in political theory and religious-oriented populist political strategy. A cult of personality is said to have developed around Khomeini after the Iranian Revolution, and Khomeini is officially known as Imam Khomeini inside Iran and by his supporters internationally. In Iran, his gold-domed tomb in Tehran's Behesht-e Zahrāʾ cemetery has become a shrine for his adherents, and he is legally considered "inviolable", with Iranians regularly punished for insulting him. While he publicly spoke of Islamic unity and minimized differences with Sunni Muslims, he is accused by some of privately rebuked Sunni Islam as heretical and covertly promoted an anti-Sunni foreign policy in the region.