TEHRAN (Reuters) - Grand Ayatollah Hossein Ali Montazeri, who died aged 87, was once the designated successor to spiritual leader Ayatollah Ruhollah Kohmeini but fell from grace with Iran's leadership after clashing with hardliners.
Montazeri, who fiercely denounced June's disputed presidential election as fraudulent, avowed that Iran's Islamic system had been abused to deny the president real authority, handing the power instead to the Supreme Leader.
An architect of the 1979 Islamic revolution that toppled the shah, Montazeri's star waned after he criticised Iran's rulers and was under house arrest in the city of Qom from 1998 to 2003.
A close ally of Khomeini before the revolution and jailed several times by the shah's police, Montazeri in recent years was among the harshest critics of a ruling clerical establishment in which splits have widened since the election.
In August, the ayatollah said on his website that the authorities' handling of street unrest following the election "could lead to the fall of the regime" and he denounced the clerical leadership as a dictatorship.
An indication of Montazeri's early political standing was a publicised meeting he had with Khomeini in Dec. 1987 immediately after the latter handed a revised political will -- believed to contain his choice for a successor -- to close aides.
Zan-e Rouz magazine quoted Khomeini as saying of Montazeri: "He is the fruit of my life. My essence is in him, not once or twice but several times."
Montazeri, one of the authors of Iran's constitution, had been expected to inherit the ayatollah's sweeping powers despite questions over his suitability and the execution in 1987 of a relative-in-law for murder and subversion.
Khomeini's son and aide Ahmad endorsed Montazeri in 1983 as the most suitable successor, and two years later the Assembly of Experts, a council of senior mullahs, also recommended him.
His political statements concentrated on rationality, justice and decency, as reflected in letters released in Paris and said to have been written to Khomeini in July 1988.
In these letters, Montazeri was said to have appealed for a halt to "thousands of executions" in which "many ... innocents and minor offenders" were killed.
Montazeri's leadership qualifications were hurt by not being a seyyed, or black-turbaned descendant of the Prophet Mohammed, as was Khomeini and as is Supreme Leader Ayatollah Ali Khamenei.
In accepting Montazeri's resignation in March 1989 after he was forced out by hardliners, Khomeini said he had been opposed to Montazeri's appointment from the beginning.
Political analysts said at the time that Montazeri's removal was a big boost for radicals like the then prime minister, Mir Hossein Mousavi, who is now the main opposition leader.
Montazeri helped develop the political system in Iran, which is based on a theory called the "rule of the jurisprudent" that says clerics should directly supervise political life.
In an interview with Reuters in 2005, he said the constitution he helped to write had not only been misused but was also flawed -- a mistake he put down to inexperience.
He said it should be changed to give the president control over state matters, including the military, police and media.
"There is a contradiction in our constitution. It gives a lot of responsibilities to the president without giving him enough authority," Montazeri said.
"Responsibility and authority should come together. You cannot give responsibility to someone without giving him authority."
He said Iran's Supreme Leader should limit his role to religious matters and to ensuring that laws conformed to Islam.
Montazeri was born into a farming family in 1922 (the exact date is not known) in Najafabad in central Iran, and started theological studies at the age of 10.
He took his early lessons in Isfahan and then in the Shi'ite holy city of Qom, south of Tehran, where he became a teacher at the age of 30.
In Qom he met, and became a disciple of, Khomeini. He joined protests called by Khomeini in his first big confrontation with the late shah's Westernisation campaign in 1963 over votes for women and land reform.
Montazeri also had his share of tragedy. One son died in a bomb blast at Islamic Republican Party headquarters in 1981; another, Saeed, lost an eye in the Gulf war in 1985, and a grandson was killed in the war in 1986.
Little is known about his private life, but Ayatollah Mohammad Guilani once said: "Ayatollah Montazeri is meticulous about, if not obsessed by, cleanliness."