Ayatollah is a title conferred on Shia Muslim clerics who are considered expert in Islamic studies. It's literal meaning is "Sign of Allah" The title of Grand Ayatollah is reserved for those who have reached the very highest standards of expertise in Islamic jurisprudence. In the West the term has become synonymous with Ayatollah Ruhollah Khomeini who led the revolution that overthrew the Shah of Iran, Mohammmad Reza Shah Pahlavi in 1979. The current Supreme Leader of Iran is Grand Ayatollah Ali Khamenei.