No state has extracted more benefit from the chaos and anarchy of the Middle East’s wars than the Islamic Republic of Iran. In conflicts from Syria to Yemen, Iran has steadily outlasted its rivals and expanded its regional influence. Those achievements owe as much to Iran’s strategic approach as to its consistency. Whereas its adversaries have been swayed to shift direction by various internal and external pressures, Iran’s ruling regime has never wavered in its policies.

That continuity is the hallmark of the Islamic Republic’s political behaviour, and is directly tied to the singular role of its ruling theocrat and supreme leader: Ayatollah Ali Khamenei. He has led the Islamic Republic since the death in 1989 of its founder, Ayatollah Ruhollah Khomeini. As the charismatic leader of the 1979 revolution, Khomeini was the architect of Iran’s transformation from a secular monarchy to an Islamic theocracy. Yet, it has been his successor, Khamenei, who, over the last 35 years, has transformed the Islamic Republic into what it is today.

From Iran’s uncompromising policies to the outsized role of its pre-eminent military force, the Islamic Revolutionary Guards Corps (IRGC), Khamenei’s influence permeates all of Iranian politics. Under Khamenei, the office of the supreme leader and the IRGC have become the yin and yang of the ruling regime. Both unelected and untouchable, these institutions, one representing the theocratic system’s religious authority and the other its coercive power, have come to define the Islamic Republic and its place in the world.

Although the complementary roles of those two institutions have determined what the Islamic Republic is, change to one or the other could likewise alter what Iran’s ruling system might become. For that reason, much attention is being paid to the ageing Khamenei and the issue of succession that will follow his inevitable death.

Khamenei is 85 years old, and though he has been rumoured to suffer from prostate cancer, there is no sense that his demise will happen anytime soon. Whether it be in a year or a decade, Iran’s political elite will face a situation that they have encountered only once before: replacing a supreme leader. How that process plays out, and who eventually replaces Khamenei, could have profound effects on the Islamic Republic, its future and that of the wider Middle East. The place of the IRGC could also be in flux, either gaining more power by becoming something akin to the Praetorian Guard of Imperial Rome or by having its influence curtailed by a new and ambitious supreme leader. Iran’s internal politics will be central to how succession plays out, but external factors, including ongoing conflict in the Middle East, could also shape the process in unpredictable ways.

As with all authoritarian states, Iran has formal ways of doing business and informal methods for shaping procedural outcomes. Formally, the issue of succession is the purview of the Assembly of Experts, an 88-member institution composed of Shia clergy, who are elected to eight-year terms by the Iranian people. As with Iran’s other elected bodies, candidates for the Assembly are vetted by the Guardian Council, an institution whose members are appointed by the supreme leader, which allows only those within Khamenei’s good graces to run. Consequently, those elected reflect the regime’s politics and ideology. In the past, Khamenei allowed a wider array of viewpoints to be represented in the Assembly, however, over the last few election cycles that has increasingly ceased to be the case. The vast majority of representatives on that body – the latest iteration of which was elected in March – come from the hardline faction of the regime, and are well in line ideologically and politically with the supreme leader and the IRGC.

The constitution of the Islamic Republic grants the Assembly of Experts an important role: should a supreme leader die or become permanently incapacitated while in office, the Assembly is tasked with electing a new one. Such a situation has occurred only once before in the Islamic Republic’s history. The death of Ayatollah Khomeini in 1989 thrust the Islamic Republic into its first leadership crisis, and the process of appointing a new one wasn’t straightforward. Originally, Iran’s constitution stipulated that only a senior religious authority (marja al-taqlid) could serve as a supreme leader. However, Khomeini had spent the early years of his office sidelining the most prominent of Iran’s remaining religious authorities and blacklisting clerical rivals. There were few politically acceptable individuals that could possibly replace Khomeini, and most of the senior clerics that remained in good standing with the regime either weren’t widely favoured by the Assembly or didn’t want the job. The Assembly also discussed replacing the leader with a leadership committee, but that idea was soon abandoned. To end a leadership crisis, the Assembly sought a compromise candidate who’d both pass muster ideologically and be willing to take the role. As Iran’s president and one of Khomeini’s closest lieutenants, Ali Khamenei fitted those requirements and was eventually chosen. However, because Khamenei was a relatively junior cleric, and lacked the credentials of a senior religious authority, the Islamic Republic was forced to change its constitution to enable the transition.

Khamenei began his tenure with a much weaker hand than his predecessor. As the founder of the Islamic Republic and its spiritual guide, Khomeini possessed a charismatic authority that was impossible to replace. He had benefitted from the adoration of his millions of supporters, and the unflinching loyalty of his cadre of students who permeated Iranian officialdom. By comparison, Khamenei lacked a popular constituency, and while he had the broad backing of the regime, he also had powerful rivals within it, including his erstwhile ally, Ali Akbar Rafsanjani, who succeeded him as president.

Needing a powerbase of his own, Khamenei aligned himself with the IRGC, whose fortunes after the end of the Iran-Iraq war (198-88) were also unclear. Khamenei became the IRGC’s champion, and fought for policies to preserve the conservative religious character of the Islamic Republic and its ideological foreign policy. In return, the IRGC used its muscle to help Khamenei sideline his opponents and crush movements for reform and social change. By the end of the 1990s, that symbiotic relationship proved effective: Khamenei’s authority was uncontested and the IRGC had become a driving force in Iranian politics.

Khamenei’s advancing age and uncertain health threatens the balancing act that has held the Islamic Republic together. That has made the issue of succession loom large within regime circles. Even though Iranian officials are generally tight-lipped about the idea of succession, they have acknowledged that the planning for Khamenei’s eventual replacement has already begun. According to the scant details that officials have shared with Iranian media outlets, the supreme leader has appointed a three-person committee from within the Assembly of Experts to do the groundwork of identifying and vetting suitable candidates for his position. The committee is composed of Rahim Tavakol, Hassan Ameli, and Ebrahim Raisi – Iran’s current president and one of the rumoured candidates for the leadership. That Khamenei is overseeing the committee’s work suggests that its ultimate recommendation will reflect his own. For that reason, should the Assembly ever vote on a new supreme leader, it is likely result will be little more than a rubber stamp for a candidate already hand-picked by Khamenei.

Khamenei cannot, however, simply dictate who will succeed him. In order to keep the regime unified and supportive of his choice, he’ll need buy-in from other power players, the IRGC first and foremost. No part of the regime, aside from the supreme leader’s office itself, has exacted more power under Khamenei’s rule than the IRGC. The supreme leader not only supports many of the IRGC’s preferred policies, he also protects them by serving as the regime’s lightning rod.

At the very least, the IRGC will want to ensure that its place within Iran’s Islamic system does not change or weaken under a new leader. It may also seek to gain an advantage from the transition. Although Khamenei has been the IRGC’s foremost benefactor, he has at times acted to constrain its ambitions. This is especially so regarding foreign policy, where Khamenei has generally favoured a gradualist approach, one that has sought to balance Iran’s assertiveness with a desire to limit escalation. The IRGC’s top brass regularly praise Khamenei for his wisdom in strategic matters, but are also decidedly less patient, and would likely adopt a more aggressive posture—and employ military force more readily—were the leader amenable.

A transition in leadership will thus be an opportunity for the IRGC to expand its control and influence within the regime. Any candidate viewed as suitable by the organisation’s commanders will be someone who, at the least, has shown unflinching loyalty to the ideological principles of Iran’s revolutionary system and foreign policy. Hawkishness toward the United States and Israel, a commitment to foreign proxies, and the prioritisation of military advancement will be minimum requirements expected by the IRGC of any potential candidate. Because such principles are broadly shared – at least outwardly – by much of the clerical establishment that remains within the orbit of Khamenei, ideological orthodoxy is not likely to be an issue of contention. Rather, it may fall to personal factors and individual relationships that sway the IRGC’s preference for this or that candidate.

Unsurprisingly, the two individuals most rumoured to be on the shortlist of potential successors fit squarely within those parameters and are known to have close personal relationships with the IRGC. President Ebrahim Raisi is the most prominent of the rumoured candidates, and with such an outward-facing role in Iran’s government, is subject to the most scrutiny. The 63-year-old Raisi has been in the orbit of the regime since the 1980s when he started his career as a young prosecutor in Tehran. His father-in-law, Ahmad Alam ol-Hoda, is a prominent cleric from Mashhad, Iran’s second largest city, and one of the most outspoken hardline personalities in the country. Raisi has similarly harboured strong conservative credentials throughout his career. He’s been a stalwart proponent of Iran’s revolutionary foreign policy and a formidable adversary of reformism and those advocating for social change – politics he continues to exhibit in office.

The other rumoured candidate to succeed Khamenei is the his 54-year-old son, Mojtaba. A mid-ranking cleric who has spent most of his career out of the public eye, Mojtaba Khamenei’s main role within the regime has been working behind the scenes as a close aide to his father. Eschewing the spotlight has allowed Mojtaba to remain above some of the regime’s fractious politics and avoid inter-hardliner feuds. His positions, however, appear to closely align with his father’s and with the IRGC. Indeed, the moments that have given Mojtaba the most public exposure, such as the crackdown on protestors in 2009, have also revealed his close affiliation with the security forces.

What typifies the candidacies of both Raisi and Mojtaba Khamenei, is their commitment to hardline politics, close association with the IRGC, and steadfast loyalty to the supreme leader. Neither is a clear front-runner, and neither the IRGC nor the supreme leader have shown an overt bias in favour of one or the other. Their potential candidacy is therefore speculative, and while both fit the bill, the ultimate decision is likely to be impacted as much by the immediate context of succession as by the regime’s preparation for it. To that extent, whenever the time comes, there will be intangible factors that could heavily shape the process of succession. Most importantly, the reaction of outside forces and the internal political environment will likely influence how succession plays out.

No matter how much the regime prepares for the eventuality of Khamenei’s death, his departure can easily spark a crisis. Many, both outside and inside of Iran, will see it as an opportunity to press for change. The Iranian people, and the Iranian diaspora, are likely to seek to exploit the power vacuum and push for reform or to call for a fundamentally different political order inside Iran. External actors might also explore ways to influence the succession process. Neighbouring states might look for ways to encourage Iran to move past the contentiousness that defined Khamenei’s rule, and embrace a new path under a more pragmatic leader. Iran’s foes could look to destabilise the regime or foment crisis within it. Either way, both internal and external factors could shape dynamics inside in unpredictable ways, and the politics of the moment could influence how the regime handles the succession.

Regardless of who is chosen, a new supreme leader will be inherently weaker than his predecessor. Were the new leader to be someone with personal aspirations, he might explore avenues to enhance his position and authority in ways that differed from Khamenei. For example, Khamenei allied with the security forces to secure his position in the regime and relied on brute force to solidify his rule. As a result, the Islamic Republic lost considerable support with the Iranian people.

There is perhaps no better evidence of this than the increasingly anti-regime tone that Iran’s episodic popular protests movements have showcased since 2009. Khamenei ruled on behalf of his constituency within the regime, and in doing so, alienated his office from much of the country. A new supreme leader could see politics differently, and perhaps, over time, gradually look to grow his support among the people. Doing so would mean compromising on the policies that the IRGC has held most dear, particularly its uncompromising foreign policy, which has kept Iran mired in a tangled web of sanctions and steeped in economic malaise. Such an approach would be hazardous, because it would mean taking on the IRGC, but were it to succeed, having the support of the Iranian people could re-energise Iran’s democracy, resuscitate the Islamic Republic’s reputation, and perhaps improve its future prospects.

A supreme leader with that type of reform-minded agenda would be a direct threat to the IRGC and to the hardliner elements within the regime. Understanding the dangers of an ambitious supreme leader is likely to compel the IRGC to take an activist approach to succession. Rather than sit on the side lines, the IRGC is more likely to make itself inseparable from the deliberation process and is central to its outcome. Beyond trying to preserve what it has, the IRGC probably recognises that the coming succession could be an opportunity for advancement. Seeking to avoid any dilution of its power, the organisation is likely to push for a candidate who not only supports its interests but also lacks obvious personal ambition. That would mean backing someone who would be content with the trappings of the office and happily comply with the IRGC’s whims.

The IRGC’s preference is therefore likely to be a candidate who will preserve the symbolic authority of the supreme leader, but also accept a weakening of the office’s practical power. A weaker leader would allow the IRGC to further expand its influence, and secure a greater voice in the country’s foreign and domestic policies. Such a scenario, wherein the IRGC exercises effective control over most levers of state, implies something that could be understood as a Praetorian system or thinly-veiled military dictatorship. In practice, that might be precisely where the Islamic Republic is headed.

The IRGC cannot simply rule Iran as a military junta. Military-centric governments, such as those in Pakistan or Egypt, don’t quite capture the role the IRGC is currently playing or might play in the future. That is because Iran’s Islamic system is defined by the office and religious authority of the supreme leader. As the self-described defenders of the Islamic Revolution, the IRGC is, above all, the guardian of the supreme leader, and it is that function which gives the IRGC its legitimacy within the parameters of the Islamic Republic and its constitution.

Therefore, the IRGC needs to maintain a clear distinction between the theocracy’s religious authority, personified by the supreme leader, and its own political influence. Were the IRGC’s authority to outwardly eclipse that of the supreme leader, the system it claimed to protect would cease to be. Further, the IRGC would lose its lighting rod, and become more readily seen by both foreign adversaries and everyday Iranians as the primary culprit of the regime’s problematic behaviour. It is for that reason that the IRGC needs the office of the supreme leader to retain authority and credibility within the regime’s construct. It doesn’t need a strong leader, but it does need that office to persist.

The regime’s structure therefore inhibits the IRGC from overtaking the supreme leader as the ruling apparatus of the nation, at least outwardly. The regime requires balance, and maintaining a semblance of balance will be necessary for any succession to succeed and for the Islamic Republic to be preserved. That suggests fundamental change is not likely, and that it will be within the grey areas of power that the IRGC will seek advantage.

The more the IRGC pushes in the contest, the more contentious and dangerous the process of succession might become. The most likely scenario is that the regime understands what is at stake, and that all major players, including the IRGC, will have agreed upon a unifying candidate well before the time for succession arrives. Yet, with innumerable factors at play, even the best laid plans can fail.