By February 1979, Ayatollah Khomeini had become the global figurehead of the Iranian Revolution, and he was to become leader of the newly formed Islamic Republic. No Muslim intellectual has achieved the same realisation of his ideas as Khomeini, with his doctrine of velayat-e faqih, or "guardianship of the jurisconsult", which stands behind the role of Supreme Leader of Iran.
This is the idea that the Twelfth Imam will ultimately return to establish divine justice, and so, in the meantime, the "guardian" of the community should be not just an expert on law, but an authority on religion. Khomeini's opponents accused him of sneaking religious authoritarianism into the Iranian constitution, and contemporary reformist theologians such as Mohsen Kadivar have argued that velayat-e faqih has no basis in Shia theology.
After Khomeini's death, there was no one with both the religious and political weight to replace him. The elevation of Ali Khamenei -- who was not yet an ayatollah, the highest tier of clerical authority in Shia Islam -- to Supreme Leader signalled the choice of political expediency over religious legitimacy in the Islamic Republic, creating the constitutional crisis that continues today.
On agreeing to the ceasefire with Iraq:
I repeat that the acceptance of this issue is more lethal for me than poison; but I surrender to God's satisfaction. I have drunk this for the sake of God's satisfaction.