The Islamic Revolutionary Guards Corps: A defensive weapon turned offensive

Explainer: A military force created after Iran's 1979 revolution conducts operations at home and abroad

In this Sept. 22, 2014 file photo, members of the Iran's Revolutionary Guard march during an annual military parade at the mausoleum of Ayatollah Khomeini, outside Tehran, Iran. AP

As an exiled cleric, Ayatollah Ruhollah Khomeini spent his wilderness years planning what an Islamic Republic would look like. By the time he returned to Iran, thunderously in 1979, he had decided that security would not be left to military men who had served Shah Mohamed Reza Pahlavi.

Instead, he founded a force of guardians who would be loyal to him. Calling them the Islamic Revolutionary Guards Corps (IRGC), drawn from the pious and often poorest Shiite neighbourhoods, their job was to protect the new republic from any threat at home or abroad. In the past 40 years it has done both.

Until his death in 1989, the force answered to Khomeini. And ever since its commander-in-chief has been supreme leader Ayatollah Ali Khamenei. The stipulation that the IRGC reports to a religious leader rather than the country's elected president is testament to two things: Khomeini’s paranoia about a coup being led by men in uniform still loyal to the Shah, and his determination that the revolution never be undone.

The IRGC's principal task – from inception – is that Iran remains an Islamic Republic.

The IRGC, which is said to number about 120,000 among its land, air and naval divisions, established its credentials as a fighting force during the Iran-Iraq War. Defending the country – into a stalemate against the much-better supplied forces of Saddam Hussein – naturally endeared its members to Iranians.

Those who died – always referred to as martyrs – are commemorated on murals in cities, particularly in Tehran. The reverence is sincere among all Iranians. Much more contentious are the IRGC's activities abroad. The bombings of the US Marine barracks and the American embassy in Beirut, attributed to Lebanon's Shiite militia Hezbollah, were made possible by Iranian support and training.

Numerous assassinations abroad have been blamed on the IRGC's elite foreign wing, the Quds Force headed by Maj Gen Qasem Soleimani, the man who has overseen Iran’s campaign in the Syrian war. But the US-led invasion of Iraq in 2003 would lead to anti-US militias receiving Iranian training and weapons that would later kill American forces. The IRGC's organisational and fighting skills were pivotal to saving Syrian President Bashar Al Assad's regime.

As is usually the case, the Iranian force operated in the shadows, initially denying any role at all in Syria. When it no longer could do so it downplayed its influence before conducting a calibrated attempt to capitalise on its appeal among a nationalist audience at home.

The role of the IRGC in Iran's economy, however, has never been popular among the wider Iranian population. Corruption is endemic. US and European sanctions imposed during the presidency of Mahmoud Ahmadinejad (2005-2013) – on account of Iran's nuclear programme – increased the IRGC's clout as it controlled borders and expanded its business interests.

Iran's subsequent president, Hassan Rouhani, is an unpopular figure among the IRGC's highest echelons as he has tried to limit their non-military activities but he has always been one step behind what has become an economic leviathan. The IRGC knows that Iranian presidents come and go, while the supreme leader – Iran has had only two in 40 years – will remain its only master.

The US designation of the IRGC as a foreign terrorist organisation could hit its economic interests. But it could also awaken the defensive instincts that Khomeini considered the force's reason for being. If the latter happens, the Quds Force would be at the forefront of any attempt to inflict damage on any forces deemed a threat.