The Islamic Revolutionary Guard Corps (IRGC) was set up on the orders of revolution leader Ayatollah Ruhollah Khomeini shortly after the 1979 ousting of the shah, with a mandate separate from the regular armed forces to protect the revolution from internal and external threats.

Over the decades, it has become a vast structure that wields not just military influence but economic power, its tentacles reaching deep into every aspect of life inside Iran.

Analysts say its influence increased under the rule of supreme leader Ayatollah Ali Khamenei, who was killed in an Israeli strike at the start of the war, and will only get stronger if his son and successor Mojtaba Khamenei survives in power.

Mojtaba, who for years was an influential but behind-the-scenes power broker in his father's office, is seen as being close to the Guards, who may have also shown their influence in his election by the Assembly of Experts clerical body.

"Its strength has been growing for decades and it has effectively become the key actor in a range of domains, namely security, and to a lesser extent the economy," said Farzan Sabet, a managing researcher at the Geneva Graduate Institute.

"In post-Ali Khamenei Iran they are now likely, and more nakedly, also the key political actor. The rapid elevation of Mojtaba Khamenei as the new leader, who is said to be closely aligned with the Revolutionary Guards' views and interests, may be an illustration of this," he added.

- 'Economic and military power' -

He also pointed to reports that Mojtaba Khamenei "allegedly got the top spot through an intimidation campaign by the IRGC Intelligence Organisation of some hesitant members of the Assembly of Experts".

Despite the tumultuous changes in Iran's leadership over the last fortnight, the Guards have remained in a state of constant activity, with their various branches releasing statements boasting of new strikes against Israel, enforcing a de-facto blockade of the Strait of Hormuz and warning Iranians against cooperating with foreign powers.

Beyond its own internal intelligence organisation, the Guards' various branches include the Basij volunteer paramilitary force and the Quds force, which is in charge of operations abroad.

Known within Iran as "Sepah" (The Corps) or "Pasdaran" (The Guards), the IRGC has over the last years built its own empire of economic interests, particularly in the energy sector, as it seeks to subvert international sanctions.

Its continued operations come despite the successive killings of its commander-in-chiefs Hossein Salami in Iran's war with Israel in June last year and Mohammad Pakpour in the current US-Israeli strikes.

Deputy commander and former interior minister Ahmad Vahidi is seen as the next Guards chief, although his appointment appears yet to be formally enshrined, possibly as a security measure given the fate of his predecessors.

The US-based Human Rights Activists News Agency said Vahidi's name has "drawn attention in recent years in connection with serious human rights violations and international legal cases", notably the 1994 bombing of a Jewish association in Argentina where he was named as a suspect.

"The IRGC is not a centralised body so you can't really speak of them controlling the country as a unified organisation," said Arash Azizi, a postdoctoral associate and lecturer at Yale University.

"But indeed networks and circles of the Guards have entrenched themselves and now control much of economic and military power in Iran. Any attempt to wrest power from them would likely need co-optation of at least some of them," he told AFP.

- 'Damaged facilities' -

Another key figure in the structure appears to be parliament speaker Mohammad Bagher Ghalibaf, a former Guards commander who, for now, has survived the strikes.

Analysts see him as playing a key role in the war effort.

"Nominally, he is just speaker of the parliament. But he enjoys broad support in the ranks of the IRGC -- a rare figure whose portfolio crosses between military, security and political functions of the regime," said Azizi.

The sheer prominence of the Revolutionary Guards have, however, made their infrastructure and the commanders major targets in the war.

"Israeli and American strikes have damaged missile facilities, military infrastructure and assets linked to the Revolutionary Guards," said Sanam Vakil, director of the Middle East and North Africa Programme at the UK-based Chatham House think tank.