He was born on Monday, the 12th Shawal, 260/July 31, 873 in the town, called Askar-i Mukram (or Askar wa Makrum), situated between the rivers of Masrukan and Shushtar. It is to be noted that Askar-i Mukram took its name from the camp (askar) of Mukram, an Arab commander sent into the Khuzistan by Hajjaj bin Yousuf.
His name was Abdullah al-Mahdi and assumed the Imamate at the age of 8 years. His father, Radi Abdullah had assigned the control of organization to his uncle, Sa'id al-Khayr. By the time al-Mahdi became young, and married a daughter of his uncle, who died after some time. On that juncture, al-Mahdi was at the age of discernment to take over complete control of organization in his own hands.
The first thing that al-Mahdi did was to summon dai Abul Hussain bin al-Aswad and insisted him to stay in the town of Hammah, and said to him, "I appoint you to be the head of all dais; whomsoever you make a headman, he shall be the headman, and whomsoever you make a subordinate, he shall be a subordinate. You shall reside on the road to Egypt." With this new mandate, dai Abul Hussain reorganised the mission at his disposal.
Jafar bin Ali, the chamberian of the Imam's household, has left behind a memoirs, entitled "Sirat-i Jafar" (comp. 346/957), and it can be seen from it that al-Mahdi was known in Salamia as a wealthy prince. He lived in the town in a huge building which had an underground passage dug underneath. This secret passage covered a distance of twelve miles and opened out at an unscathed distance from the gate of the town, its entrance at the other end being always kept covered with earth. The subterranean passage was intended for the dais and other followers in the confidence of al-Mahdi, and the entrance was opened to them at night only.
The backward Katama Berber land of the farther west of North Africa was the land of the lost cause of Islam, where Imam Jafar Sadik is reported to have sent his two missionaries, Halwani and Abu Sufiani, who laid the foundation of the Ismaili dawa in North Africa, and promulgated among the aboriginal Berbers in the territory covered by modern Tripoli and Tunisia. Ibn Khaldun (d. 808/1406) writes in his "Tarikh" (5th vol., p.89) that, "Jafar Sadik sent his missionaries to Maghrib, saying that it was a barren soil and that it ought to be watered in expectation of the person who would come to sow the real seed." We must not lose a sight of the fact that it was a prediction for al-Mahdi, who made an extensive journey and manifested in Maghrib, where he founded the Fatimid Caliphate.