The word 'Fatimid' was derived from the name of the daughter of Prophet Mohammad (Pbuh). She married Ali Ibn Taleb, who was the Prophet's cousin and son-in-law. According to the Shiites principle, the Caliph should be one from the family of the Prophet and the sons of Ali. The leaders of Shiites escaped from the Ommeyade and later from the Abbassid persecution and went to Barbary, where they were welcomed by the Kitama Tribe.
Barbary had not any connection with the Caliphate, but this province was under the Aghlabid Dynasty and the Alides joined to Idrisid Dynasty. Then, Abdullah El-Shi' I, the new leader of the Shiites succeeded in preparing an army of 200,0000 men and went to Barbary. After several battles, he completely defeated the Aghlabid prince and the Aghlabid Dynasty came to an end. Abdullah El-Shi'I declared "Obeydallah el-Mahdi the Caliph and Chief of Islam."