Who was Yahya Sinwar? Israeli military says it killed Hamas leader responsible for Oct. 7 attacks.

The Israeli military claims it killed top Hamas leader Yahya Sinwar during a military operation in the southern Gaza Strip on Wednesday.

Sinwar had been credited with being the mastermind behind the Oct. 7, 2023, Hamas attacks, during which over 1,100 people were killed and 250 were taken hostage. It was the deadliest attack against Jewish people since the Holocaust.

Israel Defense Forces said in an X post on Oct. 17 that they were investigating whether Sinwar was one of the three terrorists killed during a patrol in Gaza. The Associated Press reported that Israel was using Sinwar's DNA, which is on file from his time in prison, to determine whether he was one of the terrorists killed. The IDF stressed there were no hostages in the area.

Hours later, the IDF posted that they had “eliminated” Sinwar.

"The assassination of Sinwar will create the possibility to immediately release the hostages and to bring a change that will lead to a new reality in Gaza — without Hamas and without Iranian control," Foreign Minister Israel Katz said in a statement, according to the AP.

Hamas has not yet made a public statement regarding the reports.

Sinwar’s death is the most significant assassination of a Hamas official since Mohammed Deif, the group’s military leader, and Ismail Haniyeh, Hamas’s political leader, were both killed in July.

President Biden called it a "good day for Israel, for the United States, and for the world" now that Sinwar was dead, saying in a statement that the Hamas leader "was responsible for the deaths of thousands of Israelis, Palestinians, Americans, and citizens from over 30 countries." He compared his death to what Americans felt after al-Qaida leader Osama bin Laden was killed in 2011.

Vice President Kamala Harris told reporters that Sinwar "had American blood on his hands" and "justice has been served."

Sinwar, 61, had been involved with Hamas since joining the group in the early 1980s and took over as the head of the political bureau within the organization in July after former leader Haniyeh was assassinated in Iran.

Sinwar and Deif are believed to be the architects behind the Oct. 7 attacks. Both Sinwar and Deif had been designated as global terrorists by the U.S. State Department since 2015.

As of reporting in August, Sinwar had not been seen publicly since the attacks. In December, Israeli Prime Minister Benjamin Netanyahu said the IDF had surrounded Sinwar’s home, but it was discovered that Sinwar was hiding in the network of tunnels beneath Rafah in southern Gaza. Israel reported they killed Deif in an airstrike in July.

“He chose to send the butchers into our bedrooms to kill our babies,” Lt. Col. Peter Lerner, a spokesman for the Israeli military, told NBC News of Sinwar in 2023. “And when they chose to go full front against Israel, they signed their own death warrant. A dead man walking. We will get to that man.”

On Thursday, Netanyahu said that Sinwar's death marks "the beginning of the end" of the war in Gaza.

"The war, my dear ones, is not yet over," he said, adding that while Sinwar is dead, it doesn't mean "that means whoever replaces him will agree to a ceasefire but it does remove what has been in recent months the chief obstacle to getting one."

The New York Times reported in early October that Sinwar was blocking ceasefire and hostage exchange deals, and U.S. negotiators thought he, and therefore Hamas, had no intention of reaching a deal with Israel.

In September, Danny Danon, Israel’s ambassador to the United Nations, told France 24 that Israel was “determined” to capture or kill Sinwar and that the nation has “no intention to stay in Gaza” after that is accomplished.

After speaking to Netanyahu, Biden told reporters: "Now's the time to move on. Move on, move towards a ceasefire in Gaza, make sure that we are moving in a direction that we're going to be able to make things better for the whole world."

During a campaign event in Milwaukee, Harris said, "This moment gives us an opportunity to finally end the war in Gaza."