What began as demonstrations over economic grievances has escalated into a crisis of legitimacy for the Islamic Republic of Iran.
The anti-government unrest that started on December 28 has spread rapidly across the country of 93 million people, with US President Donald Trump openly urging Iranians to "keep protesting and take over state institutions".
The state response has been brutal. US-based human rights monitor HRANA says 2,500 protesters have been killed, while Iran International, a group of journalists based in London who oppose the regime, claims the death toll is as high as 12,000.
As the violence intensifies and Mr Trump threatens military action, a critical question is emerging: who could lead Iran if the regime collapses?
Names frequently raised include an exiled prince, a former president, and the leader of a leftist movement — but experts say no single figure has the power and legitimacy to take control alone.
What happens next could hinge on how the regime responds, the ability of protesters to divide the religious leadership, and the influence of foreign powers.
Here's a breakdown of the main players and factions that could shape Iran's future.
Who really holds power in Iran?
Iran has been ruled by the Islamic Republic since 1979 when the Islamist revolution overthrew the US-backed king, Mohammad Reza Pahlavi.
At the top sits the Supreme Leader, Ayatollah Ali Khamenei, who holds ultimate political and religious authority. Powerful clerical bodies oversee key institutions, including the judiciary and military.
Alongside these religious power centres Iran also has elected entities, such as a president — currently Masoud Pezeshkian — and a parliament.
However, candidates for office must first be approved by the Guardian Council — an unelected body that has previously weeded out those deemed disloyal to the clerical establishment.
Now, despite mounting pressure, experts say the regime's core institutions remain united, making a sudden collapse in the short term unlikely.
While Iran has weathered waves of unrest over disputed elections and economic hardship before, Deakin University research fellow Ali Mamouri says this moment is the "most critical".
"Because they [protesters] are demanding regime change," he says.
"But, having said that, just having protesters on the street doesn't mean that the regime would collapse. The regime structurally is still functional."
Who could take over?
Even if protesters were to succeed in toppling the Islamic Republic, experts say there is no obvious successor waiting in the wings.
Iran's opposition movement is "deeply fragmented" says Australian National University senior lecturer in Iranian studies Alam Saleh.
Opposition groups — both inside Iran and in the diaspora — are disjointed, pursue different goals, and vary widely in organisation. Some have identifiable leaders, while others do not.
So far no single figure inside Iran has emerged as a clear opposition leader during the ongoing protests..
According to Dr Mamouri, who has previously served as strategic communication advisor to the Iraqi prime minister, this is the result of decades of systematic repression.
"The Iranian regime eliminated all rational opposition," he says.
"They either put them in prison, forced them to leave the country, isolated them, or assassinated their character."
As a result, Dr Mamouri says few viable alternatives remain.
"The two main opposition groups are both located outside Iran, far away historically and contextually," he says.
He is referring to Iran's former monarchists and the People's Mojahedin Organisation — an exiled leftist group with a history of armed struggle against both the monarchy and the Islamic Republic.
Observers have also floated the name of former president Hassan Rouhani, though his prospects remain limited.
For more on the key contenders, click through the cards below.
The exiled prince
One name that resurfaces during periods of unrest is Reza Pahlavi, the former crown prince of Iran.
Now 65, Mr Pahlavi was a teenager when his US-backed father — the last king — was deposed in the 1979 revolution. He has lived in exile ever since.
According to Middle East scholar Kylie Moore-Gilbert there is an "influential cohort of Iranians" in the diaspora, and some inside Iran, who see Mr Pahlavi as a potential future leader of Iran.
Mr Pahlavi himself has said he would act as a transitional figure. In a recent opinion piece published in The Washington Post, Mr Pahlavi put himself forth to serve the people of Iran.
"Not as a ruler-in-waiting, but as a steward of a national transition to democracy," he wrote.
"I do not seek power, but instead aim to unify Iran's democratic forces and facilitate a peaceful transformation."
However, Dr Moore-Gilbert says Mr Pahlavi remains "a divisive figure".
ANU academic Dr Saleh says this is partly because many Iranians are wary of the return of a monarchy.
"Opposition groups, including the monarchists, are deeply reliant on foreign interference and interventions, particularly Israel's support of monarchists in Iran," he says.
"This is something that will not be accepted — at least by a very important part of the Iranian political spectrum."
Dr Mamouri also questions whether Mr Pahlavi has enough support inside Iran.
"A few chants of support do not amount to a social base," he says.
"Not to mention there is not any organisation, no clear channel, and no vision for the future."
US President Trump has also expressed doubts over Mr Pahlavi.
"He seems very nice, but I don't know how he'd play within his own country, and we really aren't up to that point yet," he said.
"I don't know whether or not his country would accept his leadership, and certainly if they would that would be fine with me."
The leftist dissident
Led by Maryam Rajavi, the People's Mojahedin Organisation (PMO) is seen by some analysts as one of the more controversial opposition groups.
Deakin's Dr Mamouri describes the leftist group as a "much more dangerous" force within Iran's fractured opposition landscape.
The PMO was once listed as a terrorist organisation by the US, accused of killing US personnel in Iran in the 1970s and of collaborating with Saddam Hussein during the Iran-Iraq war.
The group initially took part in the 1979 revolution that overthrew the Western-backed monarchy, but later broke violently with Iran's clerical rulers.
The US removed the group, which is now based in Europe, from its terrorism list in 2012, citing its renunciation of violence, though it has continued to raise concerns about the organisation's internal practices and its treatment of members.
In a recent op-ed in the UK's Telegraph newspaper, Ms Rajavi rejected the idea that change in Iran could come from foreign powers.
"The real solution lies in the organised resistance and the people's uprising," she wrote.
"There is no need for foreign military intervention or financial and arms assistance. Regime change is solely the responsibility of the Iranian people."
Ms Rajavi claims the PMO's so-called "resistance units" have been the driving force behind recent protests, and have played a key role in confronting security forces.
Ms Rajavi says her broader coalition, the National Council of Resistance of Iran, does not seek to hold power permanently.
Instead, she has proposed a six-month transitional period after the regime's fall, followed by free elections to form a constituent assembly.
That body, she says, would draft a new constitution for a democratic and secular republic, with commitments to gender equality and separation of religion and state.
The ex-president
Former Iranian president Hassan Rouhani has been cited as a potential compromise figure, but experts are skeptical about whether this is what Iranians want.
Mr Rouhani, who served two terms from 2013 to 2021, was a relative moderate within the system and played a central role in negotiating the 2015 nuclear deal with world powers.
"Rouhani belongs to the reformist camp," Dr Mamouri says.
"The reformists have long been an alternative within the regime, offering different policies and securing very big victories in past elections."
In 2017, for example, Mr Rouhani won re-election with over 23.5 million votes, while his rival trailed on 15.8 million.
He also made history in 2013 for becoming the first Iranian leader to speak directly with a US president, then Barack Obama. But Mr Rouhani's outreach to the West angered hardliners within the political establishment.
Dr Mamouri says Mr Rouhani is unlikely to emerge as a unifying leader because many Iranians are seeking something "completely different".
"The frustration and accumulation of anger, and the people's dissatisfaction, has made them move on from even the reformists," Dr Mamouri says.
"The people are now calling for something much more radical, which is regime change. They do not want to bring in the same people from the elite or a different camp from under the same umbrella."
Mr Rouhani has also remained largely silent during the current unrest and retains no independent power base, further limiting his prospects as a post-regime leader.
What comes next?
What happens next will depend on whether the Islamic Republic can reassert its grip or whether the clerical establishment will disband under pressure.
For the regime to be genuinely in danger of collapse, Macquarie University research fellow Kylie Moore-Gilbert says it needs to lose the support of key institutions like the security forces.
"What needs to happen for this peaceful movement to succeed is a splintering of the regime," she says.
"We need to see, for example, some of the security forces refusing to fire on protesters or even defecting to the side of the protesters. Or we need to see some kind of split politically within the regime."
Until then, Dr Moore-Gilbert says protesters remain "sitting ducks".
"There's been some isolated figures — clerics, for example, who would be traditionally aligned with the Islamic Republic regime — who have come out and said, 'What's happening is bad, we don't support it, we don't support killing innocent people.'
"But by and large, as of yet, we haven't seen a significant split in the regime or amongst that elite class of pro-regime supporters."
ANU's Dr Saleh says middle-class Iranians fear foreign interference, despite many of them being dissatisfied with the current regime.
"The middle class stayed at home, they didn't take to the streets," he says.
"These protests have the full support of Israel and the United States behind it, and that somehow changed the narrative amongst not only the regime, but the people themselves, and that's why we see not all Iranians are out.
"They have seen what happened to Syria, Afghanistan and Iraq. They have seen what happened to Gaza. They don't want that to happen to Iran, especially those nationalists who are deeply concerned about Iran's territorial integrity."
Dr Saleh says the collapse of the Islamic Republic could push the country into prolonged conflict.
"That would definitely lead into complete and utter chaos inside Iran," he says.
"So there will be no other alternative: the country will be facing a civil war for a decade or so to come."
Dr Moore-Gilbert also cautions against US military intervention.
"It is a double-edged sword. It could easily backfire," she says.
"It could mobilise that small but quite ideological cohort of people who do still support the regime further or it could lead to unintended consequences.
"For example, if Ayatollah Khamenei is removed, similar to what they did to Maduro [in Venezuela], who steps into the breach? And is it somebody even worse or a group of people even worse?
"It would be much more prudent for them to support the Iranian protest by restoring internet access."
