Ali Khamenei (Mohammad Ali Hoseyn Khamenei) (mōhämäd´ älē´ hōsān´ khamānāē´), 1939–, Iranian religious and political leader, b. Mashhad. A Shiite Islamic cleric who was the son of an ayatollah, Khamenei began his religious studies at a young age, and was briefly at Najaf, Iraq (1957), before he settled in Qom (1958). As an active member of the Islamic opposition to the shah from the early 1960s, he was arrested several times and imprisoned, and after 1975 was banned from teaching.

Following the fall of the shah in 1979, Khamenei became a member of the Revolutionary Council (1979) and of parliament (1980). He helped engineer the dismissal of President Abolhassan Bani-Sadr, a moderate politician, in 1981, which solidified clerical control of the government, and subsequently survived an assassination attempt. Khamenei was Iran's president from 1981 to 1989 when, with the support of Hashemi Rafsanjani he was elected to succeed the late Khomeini as Iran's supreme leader, a more powerful post than president in the Islamic republic. That year he also became an ayatollah.

Strongly anti-American and conservative, Ayatollah Khamenei has generally resisted attempts to liberalize the Islamic republic. In 2009 he lent support to President Ahmadinejad's reelection bid and strongly denounced criticism of and demonstrations against the president's victory, which were regarded by many as rigged. He subsequently (2011) clashed with the president, however, in what was regarded as a move by hardline clerics to limit Ahmadinejad's power, and Khamenei's supporters secured control of parliament in the 2012 elections.