Muhammad Al-Mahdi
Muḥammad ibn al-Ḥasan al-Mahdī (Arabic:محمد بن الحسن المهدي) (born c. July 29, 869 (15 Sha‘bān 255 AH), in Occultation since 874) is believed by Twelver Shī‘a Muslims to be the Mahdī, an ultimate savior of humankind and the final Imām of the Twelve Imams. Twelver Shī‘a believe that al-Mahdī was born in 869 and did not die but rather was hidden by God in 941 (this is referred to as the Occultation) and will later emerge with Isa (Jesus Christ) in order to fulfill their mission of bringing peace and justice to the world. He assumed the Imamate at 5 years of age. Some Shi‘īte schools do not consider ibn-al-Hasan to be the Mahdī, although the majority sect Twelvers do.
Sunnis and other Shi'ites 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 Khilafat. Sunnis also have a few more Mahdi hadiths which are not present in Shia collections.
Read more about Muhammad Al-Mahdi: Birth and Early Life According To Twelver Shi'a, The Occultation, Reappearance, Titles, Sunni View, Scholarly Observations, Consequence of Occultation of Twelfth Imam, Historicity of Muhammad Al-Mahdi