caliph of the Fatimid Caliphate (born 913)

al-Mansur bi-Nasr Allah

Abu Tahir Isma'il, better known by his regnal name al-Mansur Billah, was the thirteenth Isma'ili imam and third caliph of the Fatimid Caliphate in Ifriqiya, ruling from 946 until his death. He succeeded his father, al-Qa'im, after the latter's death, in what was likely a bloodless palace coup. At the time of al-Mansur's accession, most of the Fatimid mainland realm in Ifriqiya had been lost to a large-scale anti-Fatimid revolt led by the Kharijite preacher Abu Yazid, who was laying siege to al-Qa'im's fortified coastal palace city of al-Mahdiya. Unlike his father he was an active and publicly visible monarch, but plagued by illness, which led to his early death.