Behind the scenes of Iran's clerical authoritarian regime, cogs have been churning for years, if not decades, to ensure its survival in the event it was decapitated.
The head of the Iranian regime, former supreme leader Ayatollah Ali Khamenei, reigned over Iran for more than 30 years before he was slain by US and Israeli air strikes over the weekend.
While Ali Khamenei's followers mourn his death, a plan to replace him is already being enacted.
Publicly, there's no clear frontrunner. But amid the fog of war, a successor may have been in the making for years, according to Atlantic Council foreign policy advisor and former US naval officer Harlan Ullman.
"It's pretty clear that Ali Larijani, who has been running the country, is going to be the next leader," he said.
From the supreme leader's shadow
Ali Larijani, 67, is the secretary of Iran's Supreme National Security Council — tasked with a wide remit in Iran's constitution to preserve the Islamic Revolution, territorial integrity and national sovereignty — and has emerged as a powerbroker within the Islamic Republic.
"He's been, in essence, the executive president of the country," Dr Ullman said.
"He's been a very, very competent senior official in whom Khamenei has put a great deal of responsibility."
Larijani first joined the Iranian regime as a member of the Islamic Revolutionary Guard Corps (IRGC), ascending to senior roles before becoming a parliamentarian, leading Iran's state-controlled media, and ultimately entering the upper echelons of the Islamic Republic.
"He's done it through competence," Dr Ullman said.
Larijani has been instrumental in managing Iran's relations with key allies — he helped broker a 25-year cooperation deal with China, and has made repeated visits to Moscow to meet Russian President Vladimir Putin.
Larijani was also key to achieving the 2015 nuclear deal, which saw the United Nations, the US and the European Union lift their economic sanctions on Iran.
However, limitations on Iran's nuclear program eroded after the US pulled out of the deal in 2018 under US President Donald Trump.
Iran has long maintained its enrichment of uranium was for "peaceful" purposes, but — amid ongoing negotiations between the US and Iran — Mr Trump claimed Iran "rejected every opportunity to renounce their nuclear ambitions", and US and Israeli forces launched their assault on Tehran.
Larijani, Iran's top security official and one of slain former supreme leader Ali Khamenei's right-hand men, has sworn to take revenge.
"America and the Zionists … they have burned the heart of the Iranian nation," Larijani said on state media.
"We will burn their hearts.
"Their tyrannical methods against the [leader] of Iran, it makes the people angry … to the point that they will never forgive it."
Taking control in the chaos
Larijani has been acting as Iran's interim crisis manager while an elected panel of 88 senior clerics are tasked with the formal selection of the next supreme leader.
He's moved quickly, announcing a temporary leadership council only hours after Iran confirmed Ali Khamenei's death, and issuing harsh warnings to any potential dissenters or "secessionist groups".
Dr Ullman said there was no obvious opposition to Larijani, and the "martyring" of Ali Khamenei could embolden his leadership.
"Iran is in horrible shape — no water, no food … all their oil is being blockaded and boycotted," he said.
"So getting rid of the Ayatollah, who is really seen as responsible for this, is not a bad thing.
"Larijani, if he's smart, can exploit this by saying, 'OK, the supreme leader is gone, but we can do A, B, C and D,' which will seem to make life more palatable for the average Iranian, but really what this is doing is strengthening his rule."
One hurdle that may stand in the way of Larijani's ascent is that he's not a cleric himself, let alone a senior cleric or ayatollah.
However, he hails from one of the Islamic Republic's most politically influential and powerful clerical families — his father, Grand Ayatollah Hashem Amoli, was a renowned cleric.
And in a precedent of sorts, Ali Khamenei himself was selected as supreme leader despite not being a senior cleric at the time of his appointment.
Tipping point to revolution
Among the death toll from US and Israeli strikes are senior Iranian advisers, including the secretary of the Iranian Security Council Forces, Ali Shamkhani, and the head of Ali Khamenei's military bureau Mohammad Shirazi.
Many others among the highest ranks of Iran's military, intelligence and security leadership have also been killed.
Another potential candidate for leadership, who is still alive, is Ali Khamenei's son, Mojtaba Khamenei, a cleric.
But he has never held public office, and a father-to-son succession may be frowned upon within the clerical establishment that came to power by toppling a monarchy.
Other possibilities include the first supreme leader Ruhollah Khomeini's grandson Hassan Khomeini, as well as Iran's chief justice Gholam-Hossein Mohseni-Eje'i and Ayatollah Alireza Arafi, both senior political figures who have been appointed to the temporary leadership council.
While it's clear Iran's regime is not willing to relinquish control despite its leader's death, agitators like the United States are pushing for Iran's own citizens to throw a wrench into the inner clerical machinations.
But Director of Middle East Studies at George Washington University, Sina Azodi, said it remained to be seen whether the US and Israel's strikes could prove to be the tipping point to prompt a revolution.
"The Islamic Republic is a resilient regime … it is a major blow, but we should not expect a regime collapse very quickly," he said.
Another factor worth contemplating, Professor Azodi said, was what direction any new leadership would take.
"Will he try to follow the exact path of Ayatollah Khamenei, same ideology et cetera, or will he try to change the direction of the Islamic Republic and will adopt a more conciliatory approach to the United States?"
Dr Ullman said the potential answer to that question, if Larijani did in fact become the next supreme leader of Iran, was concerning.
"I think he would be more clever. I think he will try to make some kind of changes so that the public feels that the leadership is new, but I think ideologically, he may be more rigid," he said.
"I think his view could be, and this is what worries me most … saying, 'Look, they attacked us. They killed our leaders. Whatever you think, we need revenge'.
"I'm not sure that, necessarily, destroying the senior leadership was a good idea."
