the occultation of Imam Mahdi (PBUH) is, divided into two parts: the first, the minor occultation (Ghaybat Sughra) which began in 872 and ended in 939, lasting about seventy years; the second, the major occultation which commenced in 939 and will continue as long as God wills it.
During the major occultation till the time of his reappearance, no one has been his special representative, and there will be no one in the future, and the people have the duty to refer to the Quran, Ahl al-Bayt’s Hadith and “Fuqaha” (Jurists), those excelling in knowledge of the shariah (Islamic laws), and the narration of Hadith who are specialized in the matters of the religion.
Believe in the reappearance of the expected Mahdi (PBUH) the universal reformer is not confined to the Shia Muslims. Other Islamic groups and even non-Islamic groups like the Jews and the Christians and some of the great world intellectual figures believe in the appearance of a great spiritual reformer.