Islam / Shi'i / Twelvers / Imam /
Arabic: 'abū l-qāsimi muhammadi bni hassan
Very little can be said of him with any certainty. In fact, the non-Twelver might very well question whether there was an historical person associated with the name. Jafar, the brother of the Eleventh Imam denied the existence of any child and claimed the Imamate for himself. In fact, accounts of public appearances by Muhammad al-Mahdi often involve his mysterious arrival at key moments to challenge his uncle's claims.
In brief, the Twelver Shi'i believe that he was born to a Byzantine slave named Narjis Khatun, and that his birth was kept quiet by his father, the Eleventh Imam, Hassan al Askari, because of the intense persecution of the Shi'is at that time.
Hidden since birth, he reappeared at age of 6 to assert his claim to the Imamate, only to then disappear down a well to avoid the sad fate of his father and grandfather. For the next seventy years he maintained contact with his followers through a succession of four assistants, each known as Bab (Gate), Uthman al Amir; his son Abu Jafar Muhammad ibn Uthman; Abu'l Qasim Husayn ibn Ruh an Nawbakhti; and Abu'l Husayn Ali ibn Muhammad as Samarri. The period when he used the 4 Babs as his form of contacting the Shi'is is known as the Lesser Occultation.
On his deathbed in 941 CE, the fourth Bab, as Samarri produced a letter from the Imam stating that there should be no successor to as Samarri and that from that time forward the Mahdi would not be seen until he reappeared as champion of the faithful in the events leading to the Judgement Day. Therefore, after 941 CE there has been no earthly expression of the Imamate. This period is known as the Greater Occultation. However, it is still possible to seek the Twelfth Imam's advice or intercession by writing him a letter and leaving it at one of the Shi'i shrines. To explain the doctrine of the Occultation, Shi'i theologians draw an analogy to the idea of the sun being occulted by clouds. While the sun is out of sight, it still exists and warms the earth.
There is much that is miraculous associated with al-Mahdi. The various traditions are rich in stories and are often contradictory. Tales range from speaking from the womb, growing at so astonishing a rate that he was full grown by age 6, being raised by birds and with the ability to appear and disappear at will.
While there was much controversy over the succession of the 12th Imam, as the Lesser Occultation proceeded, dissent gradually diminished. This can be attributed in part to the active support of the Caliphate for the institution of the Bab. Several opponents of the doctrine of the Occultation were executed and others were persecuted in various ways. Another factor explaining the acceptance of the Lesser Occultation, and by extension the Greater Occultation, was that due to the house arrest of the 10th and 11th Imams. Hence, most Shi'i were already accustomed to the idea of their Imam being hidden from their view.
In the time of the 10th and 11th Imams a network of wikala (agents) had developed to act as intermediaries between the Imam and his followers, handling money and carrying messages back and forth. In fact, Uthman al Amri, the first Bab of the 12th Imam had held the same position as head of the wikala under the 11th Imam. Therefore, for most Shi'i, there was not a significant change in their relation to their Imam after the death of the Eleventh Imam.
Some titles of the 12th Imam include: Sahib az Zaman (Master of the Age), Sahib al Amr (Master of Command), al Qa'im (the one to arise), Bagiyyat Allah (remnant of Allah) and Imam al Muntazar (the awaited Imam).