The founder of the Islamic Republic maintains that emergence of the current infallible Imam, who is one of the truthful successor of the holy prophet of Islam, forms essence of particularly Shia Muslims' belief which reminds us of faith, hope, and victory of good powers over evil ones, and ultimate fortune.
The promised Mahdi, who is usually mentioned by his title of Imamu'l-'Asr (the Imam of the Period) is the son of the Eleventh Imam. His name is the same as that of the Holy Prophet.
In a hadith upon whose authenticity everyone agrees, the Holy Prophet has said, "If there were to remain in the life of the world but one day, God would prolong that day until He sends in it a man from my community and my household. His name will be the same as my name. He will fill the earth with equity and justice as it was filled with oppression and tyranny." On the Appearance of the Mahdi:
In the discussion on prophecy and the Imamate it has been indicated that as a result of the law of general guidance which governs all of creation, man is of necessity endowed with the power of receiving revelation through prophecy, which directs him toward the perfection of the human norm and the well-being of the human species.
Obviously, if this perfection and happiness were not possible for man, whose life possesses a social aspect, the very fact that he is endowed with this power would be meaningless and futile.
And the leader of such a society, who will be the saviour of man, is called in the language of the hadith, the Mahdi . In the different religions that govern the world such as Hinduism, Buddhism, Judaism, Christianity, Zoroastrian-ism and Islam there are references to a person who will come as the saviour of mankind. These religions have usually given happy tidings of his coming, although there are naturally certain differences in detail that can be discerned when these teachings are compared carefully. The hadith of the Holy Prophet upon which all Muslims agree, "The Mahdi is of my progeny," refers to this same truth. There are numerous hadiths cited in Sunni and Shi'ite sources from the Holy Prophet and the Imams concerning the appearance of the Mahdi, such as that he is of the progeny of the Prophet and that his appearance will enable human society to reach true perfection and the full realization of spiritual life.
In addition, there are numerous other traditions concerning the fact that the Mahdi is the son of the Eleventh Imam, Hasan al-'Askari. They agree that after being born and undergoing a long occultation the Mahdi will appear again, filling with justice the world that has been corrupted by injustice and iniquity. As an example, 'Ali ibn Musa ar-Rida (the Eighth Imam) said, in the course of a hadith, "The Imam after me is my son, Muhammad, and after him his son 'Ali, and after 'Ali his son, Hasan, and after Hasan his son Hujjatu'l- Qa'im, who is awaited during his occultation and obeyed during his manifestation.
If there remain from the life of the world but a single day, Allah will extend that day until he becomes manifest, and fill the world with justice in the same way that it had been filled with iniquity.