Muhammad ibn Hasan al-Mahdī (Arabic: محمد بن الحسن المهدي) is believed by Twelver Shī‘a Muslims to be the Mahdī, an ultimate savior of humankind and the final Imām of the Twelve Imams who will emerge with Isa (Jesus Christ) in order to fulfill their mission of bringing peace and justice to the world. Twelver Shī‘a believe that al-Mahdī was born in 869 (15 Sha‘bān 255 AH) and assumed Imamate at 5 years of age following the death of his father Hasan al-Askari. In the early years of his Imamate he would only contact his followers through The Four Deputies. After a 72-year period, known as Minor Occultation, a few days before the death of his fourth deputy Abul Hasan Ali ibn Muhammad al-Samarri in 941, he is believed to have sent his followers a letter. In that letter that was transmitted by al-Samarri he declared the beginning of Major Occultation during which Mahdi is not in contact with his followers.Followers of Sunni Islam and other minority Shias mostly believe that the Mahdi has not yet been born, and therefore his exact identity is only known to Allah. Aside from the Mahdi's precise genealogy, Sunnis accept many of the same hadiths Shias accept about the predictions regarding the Mahdi's emergence, his acts, and his universal Caliphate. Sunnis also have a few more Mahdi hadiths which are not present in Shia collections.The messianic belief in Mahdi helped Shias to tolerate unbearable situations to the level that without it the Shia religion might not have been able to survive persecutions in the course of history. It also acted as a moderating force among them by postponing political activities until the future coming of the Awaited Mahdi.In the biographies of Mahdi written by Shi`is themselves, it is hard to draw a line between hagiographical and historical works. In Shia sources, even in historical works of Ibn Babuya, the birth of Imam was miraculous which must be considered as hagiography. Aside from Shi`i works almost nothing is known about the life of this Imam. According to Yaan Richard some even cast doubt on his actual existence. As the messianic role of al-Mahdi, Abbasids crushing every revolt of Alids which caused al-Askari to hide the child' birth on 255/868 and just close companions get informed of the child's birth.Most scholars say al-Mahdi was born in 869 AD. His mother was reportedly called 'Narjis'. There are a couple of narrations regarding the origin of his mother. One is that Narjis was a Byzantine slave. Another narration says she was a black slave from Africa. Mohammad Ali Amir-Moezzi states that names like Sawsan, Narjis or Rayhana were common names for slaves at that time and his mother's name supports this narration. Other narration says that she was a Byzantine Princess who pretended to be a slave so that she might travel from her kingdom to Arabia. Mohammad Ali Amir-Moezzi, in Encyclopedia of Iranica, suggests that the last version is ""undoubtedly legendary and hagiographic"".