Nizar ibn al-Mustansir
Abu Mansur Nizar ibn al-Mustansir (; 1045–1095) was a Fatimid prince, and the oldest son of the eighth Fatimid caliph and eighteenth Isma'ili imam, al-Mustansir. When his father died in December 1094, the powerful vizier, al-Afdal Shahanshah, raised Nizar's younger brother al-Musta'li to the throne in Cairo, bypassing the claims of Nizar and other older sons of al-Mustansir. Nizar escaped Cairo, rebelled and seized Alexandria, where he reigned as caliph with the regnal name al-Mustafa li-Din Allah (). In late 1095 he was defeated and taken prisoner to Cairo, where he was executed by immurement. During the 12th century, some of Nizar's actual or claimed descendants tried, without success, to seize the throne from the Fatimid caliphs. Many Isma'ilis, especially in Persia, rejected al-Musta'li's imamate and considered Nizar as the rightful imam. As a result, they split off from the Fatimid regime and founded the Nizari branch of Isma'ilism, with their own line of imams who claimed descent from Nizar. This line continues to this day in the person of the Aga Khan. Life Nizar was born on 26September 1045 (5 Rabīʿ al-ʾAwwal 437 A.H.) to the ruling Fatimid imam–caliph, al-Mustansir (). At that time, al-Mustansir was around 15years old