Also known as Muhammad al-Mahdi. Eighth Ismaili Shii imam. Grandson of Jafar al-Sadiq. His succession was accepted by a minority of Shiis; the majority recognized his brother, Musa al-Kazim. Muhammad ibn Ismail's descendants became the Fatimid caliphs of Egypt. Followers recognized him in the messianic role of the Mahdi due to the Ismaili belief that there were to be seven prophets in history, each followed by a cycle of seven imams. The Prophet Muhammad was believed to be the sixth prophet, followed by Ali as the seventh. Muhammad ibn Ismail was therefore the seventh imam and final prophet, who was supposed to return to reveal truth and justice.