Islamic leader; spiritual head of the Muslims; leader of prayer in the mosque.
A religious leader must be well versed in Arabic, in the dialect of the tribe of Quraysh (Sahih Bukhari 6.507).
The Shi'ites believed in the hidden Imams. Shiites believed in 12 Imams who are the descendents of Muhammad (through Fatima and Ali b. Abi Talib). Shiites believed the Imams to be infallible.