The names of the eighth, ninth, and tenth Imams are considered by some traditions to be "hidden", known only by their nicknames due to threats from the Abbasids. The 11th Imam, Abdullah al-Mahdi Billah, founded the Fatimid Caliphate in 909 CE in "Ifriqiya" (which includes present Tunisia in North Africa), ending the first occultation. In Ismāʿīlī eyes this act again united the Imamate and the Caliphate in one person. The Fatimids then extended up to the central Maghreb (now including Morocco, Algeria and Libya). They entered and conquered Egypt in 969 CE during the reign of the fourteenth Imam, al-Mu'izz li-Din Allah, and made Cairo their capital. After the eighteenth Imam, al-Mustansir Billah, the Nizari sect believed that his son Nizar was his successor, while another Ismāʿīlī branch known as the Mustaali (from whom the Dawoodi Bohra would eventually form), supported his other son, al-Musta'li. The Fatimid dynasty continued with al-Musta'li as both Imam and Caliph, and that joint position held until the 20th Imam, Al-Amir bi-Ahkami'l-Lah (1132 CE). At the death of 20th Imam Amir, one branch of the Mustaali faith claimed that he had transferred the Imamate to his son At-Tayyib Abu'l-Qasim, who was then two years old. Tayyeb's claim to the imamate was endorsed by the "Hurrah al-Malika" ("the Noble Queen") Arwa al-Sulayhi, the Queen of Yemen, who created the office of the Dai al-Mutlaq to administer the community in the Imam's absence. Zoeb bin Moosa (d.546 AH/1151 CE) was the first Dai-ul-Mutlaq, and lived and died in Haus, Yemen. Tayyibis (which include the Dawoodi Bohra) believe the second and current period of occultation ("satr") began after Imam Tayyeb went into seclusion and Imam from his progeny is very much present as Mahdi on earth every time. The Nizari Ismailis maintain that the Shi‘a Ismaili Imams and Ismaili Muslim thinkers have explained that al-Mahdi is not a single person but actually a function undertaken by some of the hereditary Shi‘a Ismaili Imams from the progeny of Prophet Muhammad and Imam ‘Ali ibn Abi Talib.