Iran's leading dissident cleric, a defender of the nation's opposition movement and challenger of its ruling regime, died in his sleep Sunday. Grand Ayatollah Hussein-Ali Montazeri was 87. Observers say that his death could charge a seething protest movement. "Ayatollah Montazeri will be remembered in the history of Iran as brave, open-minded, and willing to say the truth at any time, even when encountering danger," one reformist cleric told the Los Angeles Times. In the 1970s, Montazeri organized religious leaders against Iran's monarchy. He was meant to follow Ayatollah Khomeini but the two had a falling out after the 1979 revolution. Since then, Montazeri served as an outspoken critic of the Islamic republic.