āyatullāh

Arabic āya (also spelled ayah or aya) meant a sign, verse, or miracle — particularly a verse of the Quran, which is divided into āyāt (signs/verses). Allāh is the Arabic word for God. Āyatullāh — sign of God — was a title indicating a scholar of such learning that his existence was a sign of divine grace. The title emerged in Shia Islam's clerical hierarchy during the 19th century.

Shia Islam developed a distinct clerical hierarchy that Sunni Islam did not: the Grand Ayatollah, the Ayatollah, the Hojatoleslam, the Mojtahed. The Grand Ayatollah (Marja-e taqlid — source of emulation) was a supreme religious authority whose rulings on Islamic law were followed by millions. This hierarchy gave Shia Islam a clerical infrastructure that could challenge and eventually replace political authority.

Ruhollah Khomeini became the most famous Ayatollah in history through the Iranian Revolution of 1979. His doctrine of velayat-e faqih — guardianship of the Islamic jurist — held that religious scholars, not secular governments, should hold political authority. The Islamic Republic of Iran was founded on this principle. Khomeini returned from exile in Paris on February 1, 1979, and the word entered every newspaper in the world.

Today Ayatollah Khamenei serves as Iran's Supreme Leader. The title ayatollah remains a term of profound religious authority in Shia Islam, carrying its original sense: this scholar's existence and learning is itself a sign from God.