THE ISLAMIC REPUBLIC OF IRAN is the only country in the world, and specifically in the Middle East, that is currently (or has ever been) ruled by an Ayatollah. (Previous Shiite Theocracies, like the Safavid Empire, were still ruled by monarchs and the Ayatollahs had an advisory role, but no direct power.)
Iran is the main Shia Moslem country
Certainly Iran. Iraq and Azerbaijan are also majority Shiite countries. Other countries like Lebanon and Yemen have large Shiite minorities.
What distinguishes Iran is that it is majority Persian ethnicity (as generally opposed to Arab ethnicity). It is also the largest Shiite Islamic-majority country (although it is not the only one as both Iraq and Bahrain are Middle Eastern countries with Shiite majorities).
Iraq and Iran
Sunni Islam and Shiite Islam cause a lot of conflict in the Middle East.
Iran is an Islamic country with the wide majority of it population are Shiite Muslims.
Iran, Iraq, Bahrain, Yemen, Lebanon.
Iran
There are actually three main sects of Islam in the Middle East. In order of size, most populous to least populous: Sunni, Shiite, and Ibadi.
Holy Shiite was created in 2004.
Prior to the Crusades, there was no "unified Middle East government". The dominant countries in the Middle East were the Abbassid and Fatimid Caliphates, which were hereditary monarchies that ruled according to Sunni and Ismaili Shiite jurisprudence respectively.