Iran will hold presidential elections on June 28, after Ebrahim Raisi was killed in a helicopter crash on Sunday.
Vice President Mohammad Mokhber has taken over as interim president, in keeping with the country's constitution.
Mr Raisi and several senior officials, including foreign minister Hossein Amirabdollahian, were killed in north-western Iran when their helicopter went down in a mountainous area. Bad weather and dense fog were to blame, the government said.
Candidates for president can register from May 30 and will be vetted by the Guardian Council, a 12-member body of clerics and jurists that administers elections.
Many Iran analysts have said the clerical establishment and supreme leader Ayatollah Ali Khamenei will probably want a president similar to Mr Raisi, a hardliner who was deeply distrustful of the US and Israel.
In recent elections, the Guardian Council has made it difficult for reformists to stand in polls.
The likely candidates
Mohammad Mokhber
Having served as first vice president under Mr Raisi since 2021, Mr Mokhber is seen as close to Mr Khamenei, who has the final say in all matters of state.
When Mr Raisi’s death was announced on Monday, Mr Mokhber took over as acting president in accordance with Iran’s constitution.
He was part of a team of Iranian officials who visited Moscow in October and agreed to supply surface-to-surface missiles and more drones to Russia's military, Reuters reported at the time.
The team also included two senior officials from Iran's Islamic Revolutionary Guard Corps and an official from the Supreme National Security Council.
Mr Mokhber, 68, previously led Setad, an investment fund linked to the supreme leader.
The fund's full name is Setad Ejraiye Farmane Hazrate Emam, or the Headquarters for Executing the Orders of the Imam.
In 2010, the EU included Mr Mokhber on a list of individuals and entities it was sanctioning for alleged involvement in “nuclear or ballistic missile activities”. Two years later, it removed him from the list.
Three years after that, the US Treasury Department added Setad and 37 companies it oversaw to a list of entities on which Washington imposed sanctions.
Mohammad Bagher Ghalibaf
Mr Ghalibaf, 62, has been the Speaker of the Iranian parliament since 2020 and was the mayor or Tehran from 2005 to 2017. He was also formerly Iran's chief of police from 2000 to 2005 and commander of the IRGC's air force from 1997 to 2000.
Should he run in this year’s early elections, it would be his fourth attempt.
In 2009, Mr Ghalibaf’s candidacy was rejected by the Guardian Council. In 2013, he was the runner-up to former president Hassan Rouhani.
In 2017, in his third attempt, Mr Ghalibaf withdrew to pave the way for a two-man battle between Mr Rouhani and Mr Raisi.
A former police chief and member of the Revolutionary Guards, he has played on his tough image in the past and campaigned against the wealthy elite.
Mr Ghalibaf lost momentum in a 2013 election bid after his rival Mr Rouhani said he had proposed allowing student protests in 1999 so that security forces could crush them.
Ali Larijani
A former parliament speaker, who held the post from 2008 to 2020, is likely to make a second bid for the presidency next month.
Mr Larijani, 65, is considered a long-time prominent conservative voice who later allied himself with Iran's relatively moderate president Mr Rouhani.
He previously came sixth in the 2005 elections when he won 5.83 per cent of the vote.
A former IRGC commander, he previously served as the minister of culture and Islamic guidance and as the head of Iran's state broadcaster.
Under hardline former president Mahmoud Ahmadinejad, he served as secretary of Iran's powerful Supreme National Security Council for two years, and as a senior nuclear negotiator.
He later became speaker of the Iranian parliament for about 12 years, stepping down when Mr Ghalibaf was elected instead.
Mr Larijani's family includes prominent members of Iran's theocracy, with his cleric brother once serving as the head of the Iranian judiciary. His father was a prominent ayatollah.
Mohammad Javad Zarif
Mr Zarif, 64, served as Iran's foreign minister from 2013 to 2021. He was educated in the US and is fluent in English.
His tenure marked a significant period of engagement with the West.
He led Iran's negotiating team in the 2015 nuclear deal with global powers, which was aimed at curbing Tehran's nuclear programme in exchange for sanctions relief.
His name has been mentioned in recent weeks after he attended the annual Tehran International Book Fair to present his latest book, The Depth of Patience, where he attracted large crowds.
Mr Zarif has blamed American sanctions on aviation parts for the crash of the helicopter that killed Mr Raisi.
“One of the culprits behind yesterday's tragedy is the United States, because of its sanctions that bar Iran from procuring essential aviation parts,” Mr Zarif said.
Saeed Jalili
Mr Jalili, 58, has dedicated his career to serving his country in various roles. He holds a doctorate in political science and has been a key player in shaping Iran's foreign policy for decades.
Mr Jalili served as Iran's chief nuclear negotiator from 2007 to 2013 and led Tehran’s delegation in nuclear talks, earning a reputation for his defence of national interests.
In the 2021 presidential elections, he endorsed hardliner and eventual president, Mr Raisi, after withdrawing only days before election day.
He is currently a member of the Expediency Discernment Council, an administrative advisory body originally set up to resolve differences or conflicts between the parliament and the Guardian Council.
He had also served in the Iran–Iraq War as a member of the Basij volunteers.
