Ali (ca. 600-661), the fourth caliph of the Arab and Islamic Empire, was the cousin and son-in-law of Mohammed. The Shiite branch of Islam regards him and certain of his descendants as inspired rulers and the only true heirs of Mohammed.

Ali was the son of Abu Talib, Mohammed's uncle and for a time his guardian. Abu Talib also was chief of the clan of Hashim of the tribe of Quraysh in Mecca. When Abu Talib was in financial straits, Mohammed took Ali into his household. Ali was there when, about 610, Mohammed received the first revelation and the call to be a prophet. Ali is said by some to have been the first male Moslem, but he could only have been about 10 years old at the time. He joined in the Hijra, the migration to Medina in 622, and shortly afterward married Mohammed's daughter, Fatima, who bore him two...