c.600 - 661
Ali ibn Abi Talib was the fourth caliph. He was a cousin of Mohammed, father of Mohammed's two grandsons Hasan and Husayn by Mophammed's daughter Fatima. He reigned from 656 to 661.
Ali was an early convert to Islam and confidant of the Prophet. A dispute over his rights to succeed Mohammed forced him into retirement. But when the third caliph - Othman - was murdered, Ali was invited by the Muslims of Mecca to accept the caliphate. He based his caliphate on ideals of social justice and equality. This led to a rebellion by the aristocracy of Mecca.
The governor of Damascus, Mo'awiya,
a kinsman of Othman's family, led a second rebellion and defeated
Ali. This led to a major split in Islam between the Sunnites and Shi'ites.
The Shia's consider him and his descendants the only true heirs of the Prophet.