Grand Ayatollah Hussein-Ali Montazeri (1922 – 19 December 2009) (Persian: حسینعلی منتظری) was a prominent Iranian Islamic theologian, democracy advocate, writer and human rights activist. He was one of the leaders of the Iranian Revolution in 1979. He was once the designated successor to the revolution's Supreme Leader Ayatollah Khomeini, with whom he had a falling out in 1989 over government policies that Montazeri said infringed on people's freedom and denied them their rights. Montazeri spent his later years in the holy city of Qom, and remained politically influential in Iran, especially to the reformist movement. He was widely known as the most knowledgeable senior Islamic scholar in Iran. and a Grand Marja (religious authority) of Shi'ite Islam.

For almost three decades, Hussein Ali Montazeri had been one of the main critics of the Islamic Republic's domestic and foreign policy. He had also been an active advocate of civil rights and women's rights in Iran. Montazeri was a prolific writer of books and articles. He was a staunch proponent of an Islamic state, and he argued that post-revolutionary Iran was not being ruled as an Islamic state.