MEMRI has an excellent synopsis of Mahdism, a must read for those seeking to understand events in Iran.
"According to Shi’ite tradition, the Twelve Imams, descendants of the Prophet Muhammad’s cousin and son-in-law Ali Ibn Abi Talib, were endowed with divine qualities that enabled them to lead the Shi’ite believers and to function as Allah’s emissaries on earth. However, when the Twelfth Imam Muhammad Al-Mahdi disappeared in 941 CE, his connection with the Shi’ite believers was severed, and since then, the Shi’ites are commanded to await his return at any time..." Read the whole thing.
"Immediately upon assuming the presidency, Ahmadinejad began to assert his belief in the imminent return of the Mahdi as the basis for his political activities. Despite the traditional belief that no one can foresee the hour of the Mahdi’s return, Ahmadinejad frequently stated that his coming was nigh, and even gave a more specific prediction.
Also: A big roundup on Iran's energy sector and its efforts to make sanctions irrelevant here.