Iran’s Supreme Leader Ayatollah Ali Khamenei was killed in strikes on Saturday by the US and Israel. The complexities of Iran’s ruling system, the ideological nature of its support base, and the power of its Revolutionary Guards make it hard to predict what might come next.

The following explains how the system was meant to operate:

WHO COULD SUCCEED KHAMENEI?

The supreme leader must be a cleric under Iran’s system of vilayat-e faqih: guardianship of the Islamic jurist. The theory holds that until the return of the Shia Muslim 12th Imam, who disappeared in the ninth century, power on earth should be wielded by a venerable cleric.

Under Khamenei and his predecessor, the founder of the Islamic Republic Ayatollah Ruhollah Khomeini, the supreme leader has the last say in all matters of state, but the system has never faced such a challenge before.

Khamenei’s sway has often been wielded through close advisers. But in the aftermath of Saturday’s strikes it is far from clear how many of those top figures have survived.

Khamenei, 86, was never publicly recorded as having named a successor and it’s not clear who might replace him if he is confirmed as dead.

His son, Mojtaba Khamenei, has at times been seen as a possible candidate but his fate is also unclear.

WILL IRAN’S THEOCRACY PERSIST?

Iran’s clerical elite control powerful bodies that extend their influence throughout the political system.

The Assembly of Experts, made up of senior ayatollahs elected every eight years, is the body that appoints the supreme leader. The constitution also gives it power to question and even dismiss a leader, but it has never done so.

In practice the choice would likely be made by the most senior figures in the Islamic Republic and then approved by the assembly. But with some top Revolutionary Guards leaders confirmed as dead, it is far from clear who would sway the decision.

WHAT ROLE COULD IRGC PLAY?

Unlike the ordinary military, which comes under the Defence Ministry in the elected government, the Islamic Revolutionary Guards Corps answers directly to the supreme leader.

Its commander Mohammed Pakpour was killed on Saturday. Formed soon after the revolution, the IRGC’s role defending the Islamic system greatly expanded during the 1980-88 war with Iraq and it is now the strongest and best-equipped section of Iran’s armed forces.

The Basij militia, a part-time paramilitary force under Guards control, is often used to quell protests inside Iran.

Still, the corps will likely play a major role in what happens to the Islamic Republic next.