Tehran: Iran's most senior dissident cleric, Grand Ayatollah Hossein Ali Montazeri, has died, his grandson said Sunday. He was 87.

Nasser Montazeri said his grandfather, who was seen as the spiritual father of Iran's reform movement, died in his sleep overnight.

Montazeri had been designated to succeed Ayatollah Ruhollah Khomeini, the late founder of Iran's 1979 Islamic revolution, but the two had a falling out a few months before Khomeini died of cancer in 1989.

Iran's current Supreme Leader, Ayatollah Ali Khamenei, succeeded Khomeini instead and has been the target of escalating criticism by Iran's opposition movement since June's disputed presidential vote.

Montazeri had repeatedly accused the country's ruling Islamic establishment of imposing dictatorship in the name of Islam.

In 1997, Montazeri was place under house arrest in Qom, 130 kilometres (80 miles) south of Tehran, after saying Khamenei wasn't qualified to rule.

The penalty was lifted in 2003, but Montazeri remained defiant, repeatedly accusing the country's ruling Islamic establishment of imposing dictatorship in the name of Islam. He said the liberation that was supposed to follow the 1979 revolution never happened.

Montazeri was one of just a few Grand Ayatollahs - the most senior theologians of the Shiite Muslim faith.

After he was placed under house arrest, state-run media stopped referring to Montazeri by his religious title, describing him instead as a "simple-minded" cleric. Any talk about Montazeri was strongly discouraged, references to him in schoolbooks were removed and streets named after him were renamed.

Montazeri was still respected by many Iranians, who observed his religious rulings or supported his calls for democratic change within the ruling establishment.

On Saturday, after months of denials, Iran acknowledged that at least three people detained in the country's postelection turmoil were beaten to death by their jailers.

The surprise announcement by the hard-line judiciary confirmed one of the opposition's most devastating and embarrassing claims against authorities and the elite Revolutionary Guard forces that led the crackdown after the vote in June.

A firm believer in democracy

Dubai: Montazeri, born in 1922, was a young disciple of Ayatollah Ali Khomeini, the father of Iran's Islamic Revolution.

His early years were spent studying religion and theology in Isfahan and later in Qom where he became a teacher.

His political views in the lead up to the Islamic revolution were anti-establishment and he served four years in prison. He was a firm believer in democracy, where an Islamic jurist acts as an advisor to the leader. Later this would come to be the Vilayah Al Faqih, or Guardianship of Islamic Jurists.

Independence

He was a firm believer, however, in the independence of the government and did not advocate the jurists to be responsible for policy making. He was against absolute rule by the religious advisors.

He played a pivotal role in the development of Iran's new constitution. Montazeri initially rejected his appointment as successor to Khomeini saying that the position should be chosen by the democratically elected assembly of experts.

Later, he agreed to the appointment. However, Montazeri began upsetting the establishment after he called for the legalisation of political parties, inquiries into the failures of the Islamic revolution, and end of exportation of the revolution.

Eventually, Ali Khameini was chosen to replace Montazeri as Khomenei's successor who now serves as Iran's spiritual leader since Khomeini's death in 1989.

What are your memories of Grand Ayatollah Hussain Ali Montazeri? How will he most likely be remembered?