A cardiac surgeon, a former mayor of Tehran and a cleric implicated in the execution of political prisoners are among the six candidates approved by officials to run in Iran’s election on Friday to replace the president who died in a helicopter crash last month.

The candidates have renounced Iran’s hijab enforcement. They’ve addressed American sanctions that have contributed to the country’s flailing economy, and openly criticized the government during a series of debates, an unusual move in Iranian politics. Still, voter apathy in the country is high and divisions among conservative leaders make predicting the outcome difficult.

Though Iran’s supreme leader, Ali Khamenei, has ultimate authority over key state matters, the president sets domestic policy and can influence foreign policy.

Iran’s Guardian Council, a committee of 12 jurists and clerics, whittled an initial list of 80 presidential candidates down to six, disqualifying seven women and a former president and many other government officials. Four candidates are still in the race.

Two of the candidates — Amirhossein Ghazizadeh Hashemi and Alireza Zakani — dropped out of the race to consolidate the conservative vote. If no candidate wins a majority on Friday, a runoff election will be held on July 5 between the top two winners.

The latest polls, published by the conservative, government-run Imam Sadiq University earlier this week showed Dr. Masoud Pezeshkian leading with approximately 24.4 percent of votes, Mohammad Baqer Ghalibaf at 23.4 percent and Saeed Jalili at 21.5 percent. The other candidates each had less than 5 percent of the vote and nearly a fifth of voters were undecided.

Here is what to know about the four presidential candidates still in the race.

Mohammad Baqer Ghalibaf

Mohammad Baqer Ghalibaf is the current speaker of Parliament and the former mayor of Iran’s capital city, Tehran. The retired pilot and Islamic Revolutionary Guard Corps commander has repeatedly run unsuccessfully for president.

He is also known for his role in the government’s violent repression of students, first in 1999 and then in 2003, when he served as the country’s chief of police and reportedly told authorities to fire live bullets on students.

Mr. Ghalibaf faced accusations of financial corruption during his tenure as mayor of Tehran and of moral hypocrisy for his family’s lavish spending abroad. He has denied the allegations.

Reportedly close to Mr. Khamenei, the conservative politician has campaigned on the promise to reduce government inefficiency, and has criticized the government for losing money by ineffectively navigating oil sanctions.

Mehrzad Boroujerdi, an Iran expert and Dean of the College of Arts, Sciences and Education at Missouri University of Science and Technology said Mr. Ghalibaf has attempted to characterize himself as the “establishment candidate,” on the side of the elite during debates by positioning himself as the only one with the experience and capability to lead.

Masoud Pezeshkian

The only reformist candidate on the ballot, Dr. Masoud Pezeshkian is a cardiac surgeon and veteran of the Iran-Iraq war who served in Parliament and as Iran’s health minister. After his wife and child died in a car accident, he raised his other children as a single father and has never remarried. This and his identity as an Azeri, one of Iran’s ethnic minorities, has endeared him to many voters.

Reformist candidates were largely disqualified from the 2021 presidential election and parliamentary election in March. Experts say Dr. Pezeshkian was likely included to increase voter turnout among reformist party voters and Iranians who boycotted March’s parliamentary elections. The government sees high voter turnout as crucial to the election’s perceived legitimacy.

Dr. Pezeshkian was endorsed by former President Mohammad Khatami and he has expressed openness to nuclear negotiations with the West, framing the debate as an economic issue.

Saeed Jalili

Saeed Jalili is an ultraconservative former nuclear negotiator nicknamed “the living martyr” after he lost a leg in the Iran-Iraq war. He leads the ultra right-wing Paydari party and represents the country’s most hard-line ideological views when it comes to domestic and foreign policy.

Mr. Jalili said he believes Iran does not need to negotiate with the United States for economic success. Though he is likely the candidate closest to Mr. Khamenei, he presents a “totally unrealistic” assessment of Iran’s economic capabilities to the public, said Mr. Boroujerdi.

“He’s dead opposed, not only to any nuclear deal, but to any sort of opening in the West,” said Mr. Boroujerdi.

Mostafa Pourmohammadi

Mostafa Pourmohammadi is the only cleric running in this election. A former director of counterintelligence, he was a member of the committee that oversaw the execution of thousands of political prisoners at Evin Prison in 1988. He has downplayed his role in the executions.

Outspoken and articulate, he said during a debate that Iran’s biggest problem was that the government lost the people’s support and cannot arouse participation in the election.

Mr. Pourmohammadi has been critical of Iran’s support of Russia during its ongoing invasion in Ukraine, saying his country is not reaping enough benefits for providing arms to the Kremlin.

He has also invoked former President Donald J. Trump in his campaign. “Wait and you will see what will happen when Trump comes,” he said during a recent televised debate. “We have to get ready for negotiations.”

In one of Mr. Pourmohammadi’s campaign posters, he and Mr. Trump are eye to eye, staring each other down. “The person who can stand in front of Trump is me,” it reads.