In February 1979, the plane from Paris touched down at Tehran, and Ruhollah Khomeini stepped back into Iran to a crowd reported at up to five million. The Shah, Mohammad Reza Pahlavi, had already fled on 16 January, and within days Khomeini was choosing his own course, brushing aside Shapour Bakhtiar and naming Mehdi Bazargan as interim prime minister. It was the moment a cleric became the face of a revolution.

He had come far from Khomeyn in Markazi province, where he was born on 17 May 1900, or perhaps 24 September 1902 according to his brother Mortaza Pasandideh. His father, Mustafa Musawi, was murdered in 1903 when Ruhollah was still a child, so he was raised by his mother Agha Khanum and his aunt Sahebeth. From the age of six he studied the Quran and Arabic with relatives close at hand, and that early schooling never left him.

After 1920, he studied first in Arak under Ayatollah Abdolkarim Haeri Yazdi, then followed him to Qom in 1921. There he immersed himself in sharia, fiqh, philosophy, and mysticism, drawing on Mirza Ali Akbar Yazdi, Mulla Sadra, Ibn Arabi, Aristotle, and Plato. By 1928 he was giving private lessons, and by 1942 he had published Kashf al-Asrar, his first political book, attacking secularism, Reza Shah’s ban on hijab, and the old order’s anti-clerical reformers.

By the 1960s, Khomeini had become a marja and a formidable voice in Twelver Shi'ism. He opposed Mohammad Reza Shah’s White Revolution in January 1963, denounced it as an attack on Islam, and helped organise the boycott of the referendum. On 5 June 1963 he was arrested in Qom after a fiery Ashura speech at the Feyziyeh madrasa, and riots followed across Iran with about 400 dead. In November 1964, after condemning the Shah’s capitulations to American military personnel, he was sent first to Bursa in Turkey, then to Najaf in October 1965.

Exile did not silence him. In Najaf he delivered the lectures later gathered as Islamic Government: Governance of the Jurist, laying out velayat-e faqih, the rule of the jurist. By the late 1970s, cassette recordings of his speeches were circulating through Iran’s mosques, and after he reached Neauphle-le-Château near Paris on 6 October 1978, reporters, supporters, and politicians queued to hear him. He returned on 1 February 1979, said Hichi, and then drove the revolution forward against the Bakhtiar government.

The new Islamic Republic quickly hardened. The referendum of 30 and 31 March 1979 replaced the monarchy with an Islamic Republic by 98 per cent, and in November the constitution made Khomeini Supreme Leader. The hostage crisis began on 4 November 1979 when students seized the American Embassy in Tehran and held 52 staff for 444 days, with Khomeini backing them as a blow against the Great Satan. He then backed war with Iraq in September 1980, accepted a UN truce in July 1988 after saying he had drunk the cup of poison, and issued the fatwa against Salman Rushdie in early 1989.