What to know about Ismail Haniyeh, assassinated leader of Hamas' political bureau

JERUSALEM and LONDON -- Ismail Haniyeh, the Hamas leader who was assassinated early Wednesday in Iran, was a longtime antagonist of Israel who rose to become leader of the Palestinian organization's political bureau, expanded the group's footprint outside the Gaza Strip and served as a key figure in the negotiations to end the ongoing Israel-Hamas war.

He had long been accused by Western and Israeli leaders of having strong ties to the Hamas organization's miltary wing, which claimed responsibility last year for the Oct. 7 surprise attack on southern Israel. He had been detained by Israel in 1989 and spent three years in an Israel prison before eventually rising to the top of the Hamas group.

Haniyeh had been a part of talks as Israel and Hamas negotiated for an end to the fighting in Gaza and a return to the hostages held by Hamas. U.S. Secretary of State Antony Blinken on Wednesday declined to comment on the assassination or how it may affect those negotiations, saying it was an "enduring imperative to getting a cease-fire, and what I do know is we are going to work at that every day."

"All I can tell you right now is I think nothing takes away from the importance of, as I said a moment ago, getting to the cease-fire, which is manifestly in the interests of the hostages and bringing them home," Blinken told reporters in Singapore.

There has been no claim of responsibility for the assassination.

Haniyeh had led Hamas political bureau since 2017

As the civil-focused Hamas branch won in the Palestinian Legislative Council elections in 2006, sweeping into power throughout Gaza, Haniyeh was named prime minister.

Israel in 2007 accused then-Prime Minister Haniyeh of "adherence to an 'armed struggle'" against Israel. The Israeli Foreign Ministry quoted Haniyeh as saying, "We are concentrating on politics but have not abandoned our arms."

Haniyeh was dismissed after a year in office by Palestinian President Mahmoud Abbas after Al-Qassam Brigades, the military wing of Hamas, took control of the security services centers in Gaza. Haniyeh rejected the decision because he considered it "unconstitutional" and described it as hasty, stressing that "his government will continue its duties and will not abandon its national responsibilities towards the Palestinian people."

The Palestinian Authority, another civil group in Gaza, was expelled from the territory in 2007, according to The U.S. Department of State. The U.S. described the political maneuvering by Hamas as a "violent takeover."

Ten years later, in 2017, Haniyeh became leader of the Hamas political group, which by then was the "de facto ruler" in Gaza, the U.S. said. Members of the General Shura Council elected him in voting held simultaneously in the Qatari capital, Doha, and in Gaza.

Haniyeh when he came to power was in charge of the civil wing the of the Hamas organization, the branch that manages "charities, schools, clinics, youth camps, fundraising, and political activities," as the U.S. State Department described it.

The following year, in January 2018, during the Trump administration, Haniyeh was placed on a U.S. government terrorism list, an official designation that named him as an individual associated with terror. His addition on that list would allow the U.S. government to block his assets under a Bush administration executive order.

"Ismail Haniyeh is the leader and President of the Political Bureau of Hamas. Haniyeh has close links with Hamas's military wing and has been a proponent of armed struggle, including against civilians," the U.S. Bureau of Counterterrorism and Countering Violent Extremism said in a 2018 report.

A State Department spokesperson at the time said Haniyeh had "reportedly been involved in terrorist attacks against Israeli citizens. Hamas has been responsible for an estimated 17 American lives killed in terrorist attacks."

Haniyeh had in the years since then called for Arab states to stop recognizing Israel by terminating agreements to normalize relations, according to a 2023 report on international religious freedom compiled by U.S. officials.

He had lived in exile since 2019 in Qatar, an Arab country that has played a key role in the Israel-Hamas negotiations.

Rise to power from a Gaza refugee camp

Born in 1963 in the Shati refugee camp west of Gaza City, Haniyeh attended schools within and near the camp. He graduated from the Islamic University of Gaza in 1987, obtaining a degree in Arabic literature. He received an honorary doctorate from the Islamic University in 2009, according to the school. After graduating, he worked as a teaching assistant at the university, and then took over administrative affairs after that.

Haniyeh began his activity within the "Islamic Bloc," which represented the student arm of the Muslim Brotherhood, from which the Islamic Resistance Movement "Hamas" emerged.

Haniyeh was widely considered to be a charismatic, popular and pragmatic leader within the Hamas movement. He was respected by many Palestinians when he became the first Palestinian prime minister for the Hamas movement and he refused to leave his simple home at a refugee camp in the Gaza Strip.

The Hamas movement over the years lost dozens of its leaders in Israeli assassinations in Gaza, the West Bank and abroad, but those deaths have not appeared to weaken the movement. Israeli killed the founding and spiritual leader of Hamas, Sheikh Ahmed Yassin, and many top leaders in the second intifada from 2001 to 2005, but in fact did not appear to diminish the movement.

Three of Haniyeh's sons and many of his grandchildren, in addition to other relatives, have been killed in the Gaza Strip since the ongoing war with Israel broke out on Oct. 7.

ABC News' Lauren Minore and Morgan Winsor contributed to this report.