Abdullah al-Mahdi Billah, Fatimid caliph (b. 873)
Abu Muhammad Abdallah ibn al-Husayn (Arabic: أبو محمد عبد الله بن الحسين المهدي بالله) (873 – 4 March 934), better known by his regnal name Al-Mahdi Billah, was the founder of the Isma'ili Fatimid Caliphate, the only major Shi'a caliphate in Islamic history, and the eleventh Imam of the Isma'ili faith.