He took over from the regime's founding figurehead, Ayatollah Ruhollah Khomeini, when he died just over 10 years later, in June 1989.

Iran's supreme leader has the final say in all matters of state.

Therefore Khamenei's death, after almost 37 years in power, marks a major transition.

Iran latest: Ayatollah Khamenei killed

Which senior leaders have died?

In addition to Khamenei, several other senior officials were killed in US/Israeli airstrikes too.

They include Iran's army chief of staff, General Abdol Rahim Mousavi, and defence minister General Aziz Nasirzadeh.

Also killed was Major General Mohammad Pakpour, who took over as the Revolutionary Guard's top commander after Israel killed its last commander last June, and Ali Shamkhani, a top security adviser to Khamenei.

Iranian media said Khamenei's daughter, grandchild, son-in-law and daughter-in-law were killed as well.

The Israel Defence Forces also claimed it had killed Saleh Asadi, head of the Intelligence Directorate of the Khatam al Anbiya emergency command, Mohammad Shirazi, head of the military bureau, Hossein Jabal Amelian, head of SPND (Organisation of Defensive Innovation and Research) and Reza Mozaffari-Nia, a former head of SPND and former deputy defence minister.

What happens now?

A three-person temporary leadership council has been formed to govern the country, in line with Islamic Republic law.

It includes Iran's reformist president, Masoud Pezeshkian, and the hard-line head of the judiciary, Gholamhossein Mohseni Ejei.

There will also be a jurist, Alireza Arafi, who is a member of Iran's Guardian Council and head of the Basij, a volunteer paramilitary force.

Ali Larijani, Iran's head of security, said the council would be set up on Sunday.

"We had prepared for such moments and have plans in place for all scenarios, even for the time after the martyrdom of revered Imam Khamenei," said Mohammad Bagher Qalibaf, Iran's parliamentary speaker.

He added: "You'll see that after the leadership council is formed, the power and integrity of officials, defensive forces and the people will be beyond imagination."

Who chooses the new leader?

While the leadership council will govern in the interim, an 88-member panel called the Assembly of Experts will pick a new leader. Under Iranian law, that must happen as soon as possible.

The panel is made up of Shiite clerics elected every eight years and whose candidacies are approved by Iran's constitutional watchdog.

The Guardian Council is known for disqualifying candidates. It barred former Iranian president Hassan Rouhani from election to the Assembly of Experts in March 2024.

A relative moderate, he struck the JCPOA nuclear deal with world powers in 2015, from which the US, under Donald Trump, later withdrew.

Who could be the new supreme leader?

Under Iran's system of vilayat-e faqih - guardianship of the Islamic jurist - the supreme leader must be a senior leader with political and religious authority.

Khamenei's power was often wielded through close advisers. But it is unclear how many have survived, and he was never publicly recorded as naming a successor.

His son, Mojtaba ​Khamenei, a 56-year-old cleric, has been seen as a possible successor. He has never held government office, however.

That said, he has been described as a gatekeeper to his father.

He studied under religious conservatives in seminaries in the city of Qom, and is described as a hardliner with close ties to the Revolutionary Guard.

It had been thought that former president Ebrahim Raisi might seek the leadership, but he died in a helicopter crash in May 2024.

Regime change?

Donald Trump is urging Iranians to take the opportunity to overthrow the Islamic Republic, which has been accused of murdering tens of thousands of its own citizens in recent weeks.

The US president has described the death of Khamenei as the "single greatest chance for the Iranian people to take back their country".

And he has claimed that many people in the Revolutionary Guard, military and other security and police forces "no longer want to fight".

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Before the Iranian revolution Iran was ruled by a monarchy, with the king called the "shah".

Reza Pahlavi, the US-based son of the shah who was deposed in the 1979 revolution has said: "With (Khamenei's) death, the Islamic Republic has in effect reached its end and will very soon be consigned to the dustbin of history."

Any attempts to appoint a successor to Khamenei are "doomed to fail from the outset", Pahlavi added, claiming they will have neither longevity nor legitimacy.

He has urged Iran's military, law enforcement and security forces to take their "final opportunity to join the nation".

He was the country's supreme leader, and he led with supreme self-confidence.

Khamenei was killed in US-Israel strikes on Iran on Saturday.

In announcing his death, Donald Trump called him "one of the most evil people in history" and urged Iranians "to take back their Country" and bring about regime change.

Iranian state media confirmed the 86-year-old's death but did not specify the cause.

Khamenei's rise to power

Khamenei was 50 years old when he was appointed as successor to Iran's first supreme leader, Ruhollah Khomeini.

The role he inherited was already endowed with enormous control, yet Khamenei added to it. The Iran he moulded revolved entirely around him.

Iran latest: Supreme leader Ayatollah Khamenei is dead

His regime faced many protests and was deeply unpopular with many Iranians. But the network of secret informants and guards that he created, overseen by the loyal Revolutionary Guard, held sway.

Most were too scared to protest, not least because they saw what happened to those who did openly express dissent.

In 2022, for instance, protests sprang up after the death, in police custody, of Mahsa Amini, the young woman accused of violating strict dress codes.

Khamenei and his faithful security forces were violent in their response.

More than 7,000 people were killed during the unrest, according to one human rights group. Nearly 53,000 protesters were believed to have been arrested.

Yet Khamenei was as defiant as he was indifferent, saying at the time "enemies" who thought they could "uproot the tree of the Islamic Republic" were "completely wrong".

He was driven by a dogmatic certainty that there was a path that needed to be followed, regardless of the consequences.

A key part in the 1979 revolution

Khamenei was born and raised in Mashhad, home to Iran's holiest shrine. His childhood saw him receive a religious education that he combined with an interest in politics.

Khamenei joined a religious opposition movement aimed at overthrowing Iran's monarchy, many years before the 1979 revolution that would eventually usher in the Islamic Republic.

He played a key part in that revolution and was a trusted, close confidant of Ayatollah Khomeini, earning a succession of significant roles. In 1981, Khamenei survived an assassination attempt that cost him the use of his right arm. Later that year, he was elected president with 97% of the vote - the previous president had been assassinated.

Khamenei served two terms as president before assuming the role of supreme leader when Khomeini died.

He was not a clear-cut choice, lacking the religious credentials that the constitution demanded, but in the end, the constitution was changed and, despite his own protestations of unworthiness, Khamenei took on the position.

A proposal to share power among a council, in order to maintain social unity, was shelved.

A cult of personality

His decades in power were characterised by a cult of personality, which Khamenei absolutely encouraged, and by his ability to quickly load all of Iran's institutions with leaders who were absolutely loyal to him.

His decrees were absolute; loyalty was expected. Iran's economy meandered and declined, particularly as he diverted billions and billions of dollars towards developing a nuclear programme that placed him at odds with so many Western powers, and which led to punitive sanctions that hobbled his nation.

A nuclear deal was signed in 2015 to limit Iran's activities in return for the lifting of trade restrictions, but Iranians saw no improvement, again taking to the streets in frustration at life under sanctions, with now familiar personal grievances against their leader.

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The deal eventually unravelled under President Trump, leaving Iran's economy isolated and the supreme leader furious.

"Trump will die and his body will turn into ashes and food for worms and ants, but the Islamic Republic will continue to stand", Khamenei said of Trump with a typical rhetorical flourish. America was the "Great Satan" in Khamenei's mind.

Israel was the "Little Satan", the country he vowed to destroy.

The supreme leader's later years of life saw Iran form an Axis of Resistance, united against Israeli and American influence in the Middle East.

Under his watch, Iran armed Russia with Iranian-made drones to fire at Ukraine, and Tehran bankrolled its two main proxies in the region, Hezbollah and Hamas, to target its sworn enemy, Israel.

Khamenei supported Hamas's 7 October attacks and encouraged and bankrolled Hezbollah's subsequent assaults from Lebanon.

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He backed the Houthis in Yemen, as well as other insurgent groups across the region and then launched his own missile strikes on Israel. But when Israel responded, with a precision and determination that came from years of planning, Khamenei suddenly seemed to have no answers.

The furious rhetoric was still there, but the air of invulnerability seemed to have slipped away. The supreme leader's supreme self-confidence no longer seemed so assured.

The world has changed profoundly since Ali Khamenei took power. How, when and by whom he is replaced is a question of huge significance: for Iran, the Middle East and across the globe.

But the US decision to go to war with Iran without any attempt to gain international consensus - or even the endorsement of Congress - sets a dangerous precedent for the unilateral use of force to achieve foreign policy goals, which could make the whole planet a lot less safe.

Iran latest: Supreme leader Ayatollah Khamenei is dead

None of America's Western allies, including the UK, will mourn the demise of Ali Khamenei, 86, who was killed by Israeli airstrikes against his compound in Tehran on Saturday at the start of a blitz of missiles and drones launched by the US and Israel.

Yet the move - which comes less than two months after US forces launched a deadly raid into Venezuela to capture its strongman ruler - further reduces the threshold for any country to deem it acceptable to lob bombs against another sovereign state to resolve a dispute.

"We are in an era of great power politics and this is what it looks like," Rob Johnson, the head of the Changing Character of War Centre at Oxford University, told me.

The consequences of Mr Trump's Iran gamble are still playing out.

But three things are already very clear.

Firstly, this intervention - especially as it will most likely not be condemned by the UK and other NATO allies, given they hate the Iranian regime almost as much as the US - will make it a lot harder for the West to criticise the legitimacy of similar attacks launched by their opponents.

For example, Mr Putin can now brush off as double standards the fiery condemnation by Sir Keir Starmer, Emmanuel Macron and Friedrich Merz of his full-scale invasion of Ukraine even though there was no justification for the Russian attack against Volodymyr Zelensky's government - in contrast to the demonstrable threat posed by the Iranian regime to its own people and the wider region.

President Xi of China will also be watching events in the Middle East closely and most likely drawing the conclusion that he now has a far freer hand to capture Taiwan by force.

At the same time, a second certainty that world leaders will understand with renewed clarity is the importance of military strength to shore up their survival.

This is especially true for those who seek to defy whoever has the strongest armed forces - which for now at least is the US under Mr Trump.

It sets the stage for even greater militarisation of the world's most powerful countries and the need for smaller and middling powers to club ever closer together - an observation made by Mr Merz at a major security conference in Munich last month.

Finally, and perhaps most profoundly, is the undeniable unravelling of a set of international rules that evolved from the ashes of the Second World War and are upheld by the United Nations to protect the sovereignty of all countries and the dignity of all people.

With Mr Trump establishing his own so-called "Board of Peace" to rival the UN, the old world order that has existed for decades has never seemed so challenged.

As for what comes next in Iran, it is very hard to predict.

The regime is reeling from the loss of its leader and has vowed its largest ever retaliation, though Mr Trump says the response so far - with Iranian missiles and drones fired against Israel as well as Gulf states where US forces are based - is weaker than anticipated.

The US president, who likes the simplicity of bold statements, is already able to portray the mission as having achieved success following the killing of Khamenei.

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One dead and others injured at Abu Dhabi and Dubai airports

But Iran's fate is not a short, self-contained, made-for-social-media news story.

As history shows, there is huge peril in any foreign intervention and the consequences of the United States decapitating the Iranian regime will only truly be understood over time.

It comes as many flights in and out of the Middle East have been cancelled due to US missile attacks on Iran and subsequent counterstrikes targeting American bases in the region.

A post on X by Abu Dhabi Airports said the incident "resulted in one fatality involving an Asian national and 7 injuries" - but did not give a cause and urged against "circulating rumours".

Iran latest: Supreme leader Ayatollah Khamenei is dead

The Dubai incident left four staff with injuries and happened when a concourse sustained "minor damage", according to the city's media office.

Aviation sources told ​Reuters news agency one of the terminals had been damaged during ​an overnight Iranian attack.

Flights from both airports were grounded on Saturday as a precaution and are expected to remain disrupted on Sunday.

There was also a minor fire on the facade of the city's iconic sail-shaped Burj al Arab hotel due to a drone interception.

"Civil Defence teams responded immediately and brought the incident under control. No injuries have been reported," Dubai's media office added on X.

Another luxury hotel in the city was also damaged by fire earlier on Saturday - again believed to have been caused by remnants from a falling missile.

The UK Foreign Office (FCDO) has warned Britons in several Middle East countries to "immediately shelter in place" and to avoid travel to Israel and Palestine.

"Remain indoors in a secure location, avoid all travel and follow instructions from the local authorities," advised the FCDO.

It said it was "working around the clock" to support British nationals affected.

UK citizens are being urged to sign up to Register Your Presence and travel advice emails so the Foreign Office can send them information.

Thousands of Britons are potentially stuck due to the temporary closure of airspace and airports in countries such as the UAE and Qatar.

British Airways cancelled Saturday's Dubai, Doha, Amman and Abu Dhabi services, as well as flights to Tel Aviv and Bahrain up to 3 March.

A BA flight from London to Doha, Qatar's capital, was among dozens forced to turn around or divert mid-flight early on Saturday, according to flight tracking websites.

London Heathrow said "a small number of flights" had been cancelled or delayed.

Its departures board on Saturday afternoon showed cancellations including an Emirates flight to Dubai, a Qatar Airways flight to Doha, and an Etihad service to Abu Dhabi.

A Gatwick spokesperson said it was also "expecting disruption to our Qatar and Emirates flights".

Manchester Airport departures showed a Saturday night Emirates flight to Dubai had been scrapped as it shared a post advising people to check with their airline.

Wizz Air also confirmed flights between London Luton to Tel Aviv were suspended in both directions until 7 March but that "operational decisions will continue to be reviewed".

Virgin Atlantic said journeys from destinations including India and the Maldives could take longer as the routes were being altered for safety reasons.

Many other large airlines have also paused flights to the Middle East, as well as some routes flying over the region, including Delta, Lufthansa, Cathay Pacific and Turkish Airlines.

Etihad Airways said all flights to and from Abu Dhabi would be suspended until 2am UAE time on Monday 2 March.

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India's airlines are also suffering serious disruption.

Its aviation ministry said more than 400 flights by domestic carriers had been cancelled on Saturday and a similar number were expected on Sunday.

Dubai airports at standstill

The worst disruption is likely to be caused by the grounding of flights at Dubai's main airport, the world's busiest for international traffic.

People jetting out for a winter break - and the thousands who change aircraft there - are set to have their plans upended after the UAE closed its airspace.

All flights at Dubai's International, Dubai World Central (Al Maktoum) and Abu Dhabi's Zayed International have been suspended.

At least 90,000 people transfer every day in Dubai, Doha or Abu Dhabi on just three airlines, Emirates, Qatar Airways and Etihad Airways, according to analytics firm Cirium.

People in Dubai were earlier filmed running for shelter as air raid sirens sounded and witnesses told Reuters at least three big blasts were heard over the city.

A fire broke out near the entrance of the five-star Fairmont The Palm hotel after debris reportedly fell from an Iranian missile.

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A Dubai airports statement called the closures an "exceptional precautionary measure", while Emirates said safety was its "highest priority" as it halted flights.

"You have crews, planes and passengers stranded all over the world. It's a massive logistical nightmare," a Gulf airline source told Reuters.

Qatar's international airport also suspended all services after the country's airspace was locked down in case of more attacks from Iran.

People were earlier forced to run for cover as a missile - which was likely intercepted - tumbled out the sky and exploded in a residential area of Doha.

America's largest regional air base, al Udeid, is near the city and Iran has deemed all US bases in the region as fair game.

US President Donald Trump said on social media that Iran's ruler had been killed during the surprise wave of US-Israel strikes.

The death of the 86-year-old was later confirmed by Iranian state media, though it did not specify the cause.

Announcing the death, Mr Trump called the killing the "single greatest chance for the Iranian people to take back their country".

But whether the decapitation of Iran's top level of leadership would lead to regime change depends on whether people are willing to fight for it, Sky's international correspondent John Sparks said.

"The clerics and their supporters will hold on until the bitter end," he added.

In the meantime, the deep-rooted divisions in Iranian society were on full display throughout Saturday as emotions soared.

Some clips appeared to show people celebrating in the streets, cheering and honking horns. "I love Trump," says a man in one video.

Their long-simmering resentment of the regime will only have been intensified by the brutal killing of thousands of fellow dissenters seven weeks ago.

Sparks said: "Many civilians are so alienated and angry with their rulers, that you can see them celebrating this military operation."

But the US is unlikely to have won much support from the families of dozens of children killed in a strike on a girls' school.

And those already ardent supporters of the regime also went out into the streets, apparently pictured praying for themselves, their leaders and the regime.

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Ali Khamenei led Iran with supreme self-confidence

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But the rulers also have a fiercely loyal base.

Photos showed these pro-government supporters out waving flags and carrying photos of Ali Khamenei on Saturday afternoon.

Fatemeh Esmaeilkhah, a Tehran resident, said: "You martyred the Imam of our Ummah... We will make you mourn.

"We will wipe you off the earth. You think we are mourners and we are on our knees. Yes we are mourning but we haven't fallen. Hear this. We'll teach the whole world what a mistake you have made."