Since Iran is consistently in the news, I thought it would be useful to understand a little about the origins of the Ayatollahs. Heinz Halm, from the University of Tubingen, provides a sound historical background to the development of "Shia Islam - From Religion to Revolution:"
"His true name was al-Hasan ibn Yusuf ibn Ali ibn al-Mutahhar, though even many Shi'ites do not know him by this name. He is known to all Shi'ites by his honorific epithet al-Allama al-Hilli - "the most learned one of al-Hilla." He was also the first scholar to bear the title Ayatullah (sign of God). At that time it was merely an honorary name; only later was it introduced to denote a certain status within a hierarchy.
The Allama was born in 1250, shortly before the Mongol invasion. He studied in al-Hilla under his father and uncle and later went to Tabriz in Azerbaijan to the court of the Mongol Khan...Oljeitu. He even succeeded in winning the trust of the khan and converting him to shi'ism....Oljeitu had the names of the twelve imams embossed onto the coins, but this remained an isolated episode; succeeding Mongol rulers of Iran converted back to Sunnism. The Allama died in 1325 and was buried near the grave of the eighth imam in Mashad, where he is honored today as a saint.
The most significant theoretical accomplishment of Allama al-Hilli was the development of the principle of ijtihad legal ruling based on rational considerations. The foundation of the rule of mullahs in present day Iran lies in this principle.
The starting point of all theoretical considerations is how to answer questions of a religious, juridical nature if they are not definitively clarified by the Quranic revelation or a saying of an imam (a modern example discussed below is that of birth control). We recall that in Shi'ism, only fourteen persons are considered infallible: the Prophet Muhammad, his daughter Fatima and the twelve imams. Thirteen of them are dead; one is hidden and thus inaccessible. All other people are subject to error. No one can claim infallibility. What procedure must be taken if a problem cannot be solved by referring to the transmitted statements - which are limited? This is where human reason comes in: God gave human beings reason to be used to discover His will. If no answer is offered by tradition (naql) then one must gain help from the intellect (aql). A solution so reached, however, like all human decisions, is fallible and therefore subject to revision any time.
This rational effort to solve problems is expressed through the Arabic word ijtihad, a verbal noun denoting "making of an effort." The word is related to the familiar term jihad (effort, action), used to denote the struggle for the attainment of God's purpose on earth. The participle of ijtihad is mujtahid, translating approximately as "the effort-making one." This is a central term; the influence of present-day ayatolllahs lies in the fact that they are mujtahids." (1999, pp. 102-103).
~ Excerpted from "Shi'a Islam: From Religion to Revolution" By Heinz Halm.