Muhammad al-Mahdi, Iraqi 12th Imam (d. 941)
Muhammad ibn al-Hasan al-Mahdi (Arabic: مُحَمَّد بِن ٱلْحَسَن ٱلْمَهْدِي, Muḥammad bin al-Ḥasan al-Mahdī) is believed by the Twelver Shia to be the Mahdi, an eschatological redeemer of Islam and the final Imam of the Twelve Imams who will emerge with Isa (Jesus) in order to fulfil their mission of bringing peace and justice to the world. Twelver Shias believe that al-Mahdi was born on 15th Sha'ban 869 CE/ 255 AH and assumed the Imamate at nearly four years of age following the killing of his father Hasan al-Askari. In the early years of his Imamah, he is believed to have had contact with his followers only through The Four Deputies. This period was known as the Minor Occultation (ٱلْغَيْبَة ٱلصُّغْرَىٰ) and lasted from 874 to 941 CE. A few days before the death of his fourth deputy Abu al-Hasan Ali ibn Muhammad al-Samarri in 941, he is believed to have sent his followers a letter. In that letter, which was transmitted by al-Samarri, he declared the beginning of Major Occultation (ٱلْغَيْبَة ٱلْكُبْرَىٰ), during which Mahdi was not to be in contact with his followers directly, but had instructed them to follow the pious high clerics for whom he has mentioned some distinguishing merits.Most Sunni Muslims reject that he was the Mahdi and believe that the Mahdi has not yet been born. They believe his exact identity is only known to Allah and accept the idea that he is to be from the descendants of Muhammad. Aside from the Mahdi's precise genealogy, Sunnis accept many of the same hadiths which Shias accept about the predictions regarding the Mahdi's emergence, his acts, and his universal Caliphate. Sunnis also have many hadiths about Mahdi in their Hadith collections. Muhammad ibn Al-Hasan and At-Tayyib Abu'l-Qasim ibn Al-Mansur are descendants of Muhammad who are considered by different groups of Shi'ites (respectively Twelvers and Tayyibi Isma'ili-Musta'li-Isma'ilis) to be Occulted Imams and Mahdis.