Muhammad ibn Hasan al-Mahdī 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 the 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 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 belief in the appearance of Hidden Imam as the Mahdi helps Shias to endure under unbearable situations and to hope for a just future pending the return of Mahdi.

It would not be an exaggeration to suggest that without such a belief in the role of the twelfth Imam the Imammite religion might not have been able to survive persecutions under different dynasties in the course of Islamic history.

The hope in the future coming of the Imam thus became the moderating force among the Imamiya who postponed any political action pending the appearance of the Awaited Mahdi