Iranian President Ebrahim Raisi, known for enforcing brutal crackdowns on political opposition and seen as a potential successor to the supreme leader, has died in a helicopter crash landing in the country’s north, state media reported Monday. He was 63 years old.

Raisi, a conservative hard-line cleric, took office in August 2021 after several popular candidates were disqualified from the election, which had historically low turnout. He wore a black turban, symbolic of those who are descendants of the Prophet Muhammad.

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His tenure included a crackdown on mass protests after 22-year-old Mahsa Amini was killed in 2022, the enforcement of a strict women’s dress code, increased enrichment of uranium after the U.S. withdrew from a landmark nuclear deal and increased military tensions with Israel and the West as the regime supported Hezbollah in Lebanon, the Houthi rebels in Yemen and Russia’s invasion of Ukraine.

Raisi was sometimes notably referred to as the “Butcher of Tehran,” as activists accused him of being one of the four judges who oversaw the mass execution of thousands of political prisoners in 1988 after the Iran-Iraq war. Iran has never acknowledged what has been described as a massacre of an estimated 2,800 to 5,000 people, according to Human Rights Watch.

“As deputy prosecutor general of Tehran,” the U.S. Treasury Department said in a 2019 sanctions announcement, “Raisi participated in a so-called ‘death commission’ that ordered the extrajudicial executions of thousands of political prisoners in 1988.”

In 2021, when Raisi was asked about his alleged involvement in the 1988 mass executions during his first news conference as president-elect, he described himself as a “defender of human rights.”

State media reported early Monday that rescuers found “no sign of life” in the wreckage of the helicopter that made a “crash landing” Sunday. Search-and-rescue teams deployed to the scene took hours to reach the crash site, delayed by heavy fog and bad weather.

Raisi was returning with a government delegation that had attended the inauguration of a dam on the border with Azerbaijan.

Two helicopters traveling with Raisi made their destination unharmed.

Though state news aired prayers for Raisi and others following the crash, he is despised by many Iranians in the country and around the world for the government’s brutal crackdown on the country’s 2022 women-led protests and Iran’s dire economic situation. 

In 2017, he lost the presidential election to Hassan Rouhani, who was elected to a second term by a wide margin. Rouhani, who had run on a promise to reduce Iran’s diplomatic and economic isolation, was banned this year by Iran for running for the Assembly of Experts, which appoints and can dismiss the supreme leader, Reuters reported.

In 2021, Amnesty International Secretary General Agnès Callamard urged an investigation of Raisi for his alleged “crimes against humanity” while he was head of the judiciary.

Under Raisi’s watch, Callamard said, Iranian authorities killed hundreds of people with impunity, “subjecting thousands of protesters to mass arrests and at least hundreds to enforced disappearance, and torture and other ill-treatment during and in the aftermath of the nationwide protests.”

“Ebrahim Raisi’s rise to the presidency follows an electoral process that was conducted in a highly repressive environment and barred women, members of religious minorities and candidates with opposing views from running for office,” Callamard said.

In 2022, the United Nations’ human rights office opened an investigation into the violent suppression of protesters who took to the streets following Amini’s killing. She died after morality police detained her for allegedly not wearing her hijab properly and failing to adhere to the dress code.

The U.N. said in March that a fact-finding mission found Iran responsible for the “physical violence” that killed Amini, despite Iranian officials’ saying otherwise.

Raisi told NBC News’ Lester Holt last year that Amini’s death was “an incident,” alleging that similar “incidents” frequently occur in Western states. He claimed that Iran’s leadership “tolerated” the protests, despite widespread reports of violent suppression of demonstrators.

“You should be assured that the Islamic Republic of Iran has always been ready to listen to [the] words of protesters. On any issue, we are all ears,” he said through a government translator.

Raisi also claimed that there was still “freedom of speech” in Iran and denied allegations by human rights advocates that the country enforced an internet blackout after the protests. The Iranian regime is also accused of blocking social media apps, arresting journalists and punishing any public criticism of the government following Amini’s death.

He alleged that the allegations were an attempt by Western states to destabilize Iran internally.

U.N. Human Rights Chief Volker Türk said in January 2023 that Iran’s government was weaponizing the criminal proceedings and death penalty laws to stamp out dissent.

“The weaponization of criminal procedures to punish people for exercising their basic rights — such as those participating in or organizing demonstrations — amounts to state-sanctioned killing,” Türk said.

Despite concerns over Iran’s attacks on human rights, Raisi was permitted to address the U.N. General Assembly last year, when he criticized Western states for meddling in Middle Eastern affairs.

“An independent and robust neighborhood presents an opportunity for the entire region,” he said, referring to potential regional partnerships. “We will welcome any extended hand quite warmly.” 

Western leaders have long accused Iran of playing a destabilizing role in the Middle East through its support of proxy battles throughout the region.

Iran has supported Hamas militants in Gaza, Hezbollah fighters in Lebanon and Houthi rebels in Yemen for years. Israel, during its ongoing war in Gaza, launched a strike in April on the Iranian consular building in Syria, killing two of Tehran’s top commanders. Iran responded by launching a wave of cruise and ballistic missiles and drones at Israel, many of which were shot down, resulting in minor injuries.

Raisi condemned Israel’s occupation of the Palestinian territories in his U.N. speech in September, saying people see Iran as a “secure partner for their own security” just weeks before Hamas launched its Oct. 7 attack on Israel. The group took more than 200 hostages at the time, and Israeli officials have blamed it for more than 1,200 deaths that day.

Iranian officials said they were not aware of Hamas’ plans for the attack but have since repeatedly expressed support for the group against Israel.

Under Raisi, Iran continued to pursue a nuclear program that accelerated after President Donald Trump withdrew from the multilateral nuclear deal in 2018. The landmark Obama-era agreement curtailed Iran’s nuclear program in exchange for an easing of harsh economic and diplomatic sanctions.

Iran has insisted it is not pursuing nuclear weapons.

Raisi was married to Jamileh Alamolhoda and had two daughters.