Hosein-Ali Montazeri the student of Ayatollah Khomeini was an important revolutionary active against kingdom dynasty. He was jailed and tortured in Pahlavi prisons and after revolution he supported revolutionaries and it was expected for him to be the next supreme leader of Iran after Khomeini's death.
in 1987 his first oppose against leadership occured when the revolutionaries were executing big numbers of protesters. He was directly demoted by Khomeini the revolution leader. In a short time his name and books were censured from all the media. His classes were closed and regime tried strictly to not let his followers contact him. After Khomeini's death Ali Khamenei got Iran's leader while many of Shia scholars believed he is not qualified because he was not an Ayatollah and didn't wrote any book but unbelievably he got an Ayatollah title after being the leader. Ayatollah Montazeri after 90s announced Khomeini's theory is not democratic and the grand supreme leader is not innocent and might get corrupted so people must be able to choose him. In a speech in 1997 he opposed the leaders for dis-behaving with Bahai people of Iran and then announced Khamenei is totally stepping out of Islam which made the regime jail him inside of his house until his death. He has been supporting the green movement of the people of Iran after the rigged election of June 2009. He passed away in December 2009 on age 87. Today a big population of people including many of nonreligious and non Muslims were participating in his funeral while the regime was not able to prevent it.
Since Safavid Dynasty in 16th century Shia religion got the official religion of Iran. About 90% of Iranian Muslims are Shia. Through these centuries Iran was having non religious kingdoms and people according to their Shia beliefs were in touch with the Islamic scholars and observing their personal religious rituals. In 20th century the grand Ayatollah Rouhollah Khomeini brought a new theory called the Clerical Authority which means theocratic political rule by Islamic jurist. According to this theory a Shia country must have one source of emulation above other scholars who rule the society in private and political aspect of life. He was the leader of Iran's revolution in 1976 and rationally the country ended up with a very strict Islamic regime. Islamic Republic of Iran is a modern and "nonreligious" political regime with no reputation in Shia history. At the moment there is a huge opposition through Ayatollahs and Shia jurists against clerical authority in Iran. They believe Khomeini's theory was a wrong reputation from Islamic sources to make the clerics get involved with political power and take back people's life to medieval ages. The number of opposition scholars is countless but they are mainly jailed or highly monitoring by the regime.
Islam world is divided to Shia and Sunni sect. Almost 90% of the world Muslim population has Sunni faith. Foreigners usually ask me what is the difference between Shia and Sunni religion? According to my understanding I try to give a brief explanation.Islam is a monotheistic religion and Muslims believe their holly book Quran is an eternal reference for guiding human to truth and salvation. Mohammad as the messenger of G-d _and not the author of Quran_ was the only "human" who could perfectly understand and perform Quranic laws. In Sunni faith there are four guides (Imam) after Mohammad who ruled Islamic society. Shia Muslims believe the guides were 12 innocents who were only the sons of Mohammad and the last Imam called Mahdi will emerge someday to rule the world into justice and piece.The major argument between two sects is where Sunnis say after Mohammad there is no man who perceives Quran so they follow the tradition of Mohammad in his life time and also notify their four Imams as the 1st rulers of Islamic society/Ommat. That is the reason for Sunni countries to observe many of their Islamic rituals in the exact way of Mohammad time. Eventhough they may seem primitive or rigid to modern people. Shia Muslims believe Mohammad and his 12 sons had the G-d given wisdom to perceive Quranic laws and they can guide the followers but during the time Shia people are not having an Imam in present they have to get guidance for their religious life from a religious scholar who would be chosen between numbers of major Shia scholars (Ayatollah). Therefore in Shia faith there is not necessary to follow the exact tradition of Islam in Mohammad time and some changes would happen according to the time the scholars are living in. This has been the reason why Sunni Muslims blame Shia followers for being deviated from the pure traditional shape of Islam and some of them believe "Kill a Shia and get to heaven!"