Hamas' Yahya Sinwar chairs a meeting with leaders of Palestinian factions at his office in Gaza City on April 13, 2022.

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Yayha Sinwar has been a central figure in Hamas for decades and was the key figure behind the attack on Israel on October 7, 2023 and the bloody conflict in Gaza that followed the following year.

Sinwar, a short, wiry man with close-cropped hair that is now white, was known for his obsessive secrecy and security precautions and was described as a psychopath by Israeli politicians and security officials.

Sinwar's death in an Israeli strike in the Gaza Strip fulfilled a promise made last year by Israeli leaders, including Defense Minister Yoav Gallant, who vowed to assassinate him in retaliation for the wave of killings and hostage-taking that horrified Israel a year ago.

Sinwar was widely believed to be responsible for the decision to return prisoners to Palestinian territory, which irrevocably changed the course of Israeli-Palestinian history.

He had spent more than two decades in Israeli prisons before being released 12 years ago in a hostage deal like the one he hoped to broker during the current conflict.

The October 7 attack last year won Hamas's support among many Palestinians, many of whom saw it as a resistance to decades of Israeli oppression.

For the past 12 months, most Palestinians and Israelis have imagined that Sinwar was mostly underground in part of the extensive tunnel network that has plagued the Israeli military's operations in the Gaza Strip.

But his role in the on-again, off-again ceasefire talks between Hamas and Israel – brokered by the United States, Egypt and Qatar – gave him significant influence as he continued to try to outmaneuver Israel and survive.

Sinwar was born on October 29, 1962, according to Hamas, and helped found the group's internal security apparatus in the late 1980s. He earned a nickname among Palestinians: the Butcher of Khan Younis, where he grew up in the southern Gaza Strip. For years, his role in Hamas was to help track down suspected Palestinian informants for Israel.

He was sentenced to four life sentences in Israel in 1988 and was accused of participating in the killing of Israeli soldiers and four suspected Palestinian collaborators with Israel.

“He (has) so many secrets,” says his former prison mate Esmat Mansour, who now works as a current affairs commentator in Arabic-language media.

Mansour recalls that Sinwar assembled a small team of confidants who smuggled cellphones into the prison, interviewed new prisoners about how they had been caught preparing an attack on Israel, and caught Palestinian prisoners serving as informants for Israel.

“So many spies,” Mansour said during a conversation with NPR in the Palestinian city of Ramallah.

In 2006, Israeli soldier Gilad Shalit was captured by Hamas and held hostage in Gaza for five years. The man guarding the captured soldier was none other than Sinwar's own brother, Mohammed.

In 2011, Hamas released the captured soldier in exchange for more than 1,000 Palestinian prisoners. Sinwar's brother made sure that Sinwar was among them.

“All the prisoners saw him as a man who could decide their lives,” says Mansour.

His VIP status in prison and his return to Gaza with the released prisoners helped Sinwar rise to become leader of the Gaza branch of the group, which is designated a terrorist organization by several nations, including the United States.

But over the years he appeared very rarely in public and met with groups of foreign journalists only twice, and that was during times of conflict with Israel.

People are reflected in a window where a poster of Hamas leader Yahya Sinwar hangs in the Palestinian Bourj al-Barajneh camp August 8 in Beirut.

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“Your presence for us is a great achievement and enrichment for our people and our cause,” he told guest reporters at a 2018 news conference in Gaza City that lasted two hours.

At this point, Hamas was holding two Israeli citizens and the bodies of two killed Israeli soldiers. When NPR asked Sinwar about the prisoners, he said it was a confidential file that he didn't want to talk about.

During this time, Hamas encouraged violent protests along the Israeli border fence in the blockaded Gaza Strip. He said it was a strategy he learned from his hunger strikes in Israeli prisons, where he said Palestinian prisoners protested against better conditions from their Israeli prison guards.

The strategy seemed to work.

Hamas and Israel, which do not speak directly, have reached an indirect agreement known as “rest for calm.” Hamas agreed to ease hostilities, and Israel agreed to reduce Gaza's high unemployment rate by granting coveted Israeli work permits to thousands of workers from the territory.

A Hamas-Israel war in 2021 torpedoed this unofficial agreement. Sinwar gave another press conference to foreign media after the 2021 round of fighting and denied that Hamas had directed international humanitarian aid to its secret efforts to build underground tunnels for Hamas fighters.

Israeli permits for workers from Gaza resumed and rose sharply as fighting between Gaza and Israel ceased. The number of work permits Israel issued to Gaza workers before the current war exceeded 8,000.

Eyal Hulata, who served as Israel's national security adviser last year, believed this strategy gave Israel some respite on the Gaza border.

“I don't know it. I thought we understood what Sinwar was thinking, and that was so wrong,” Hulata told NPR in a recent briefing with reporters.

When Hamas militants stormed the border, killing about 1,200 people and returning at least 240 prisoners to Gaza, Israeli society and the country's political and military elite were largely confused and deeply shocked, according to Israeli officials.

Israel's military operation in response has killed more than 42,400 Palestinians and injured more than 99,000, according to Gaza's Health Ministry.

Sinwar was the leader of Hamas in the Gaza Strip at the time of the attack on October 7 last year. In August this year, he took over as the Hamas organization's top political leader after its political leader Ismail Haniyeh was assassinated in Iran, presumably by Israel.

At the time, Sinwar was one of the few remaining senior Hamas officials following the assassinations of Haniyeh, deputy political chief Salah Arouri in January and top military commander Mohammed Deif in July. Israel confirmed the murder of Deif and is said to have carried out the other attacks.

David Meidan, the Israeli negotiator who, along with other officials, agreed to Sinwar's release from prison in 2011 during an exchange in which Palestinian prisoners were released in exchange for a single captured Israeli soldier, explains Sinwar's strategy with the January 7 attack. October 2023 was similar.

“First of all, it’s about taking as many hostages as possible and using them as a tool to release his friends,” says Meidan.

Sinwar had been unable to secure the release of his fellow prisoners with whom he had spent years behind bars in Israel. But last year Israel released several Palestinian women and minors who had been detained in recent years in exchange for Hamas releasing some of the Israeli hostages brought to Gaza last October.

During this time, both sides agreed to a temporary ceasefire in the war in late November 2023. For every 10 hostages released by Hamas per day, Israel extended the ceasefire for another day and released 30 Palestinian prisoners and detainees.

Many Israelis feared that a pause in fighting would help Hamas militants regroup and allow more time for international pressure to resume Israeli military aggression. But Israel resumed fighting in Gaza after a dispute over the type of hostages Hamas offered to release, and renewed rocket fire from Gaza into Israel.

Meidan said the lull in fighting helped Sinwar buy time – crucial to his survival. After the last war between Israel and Hamas in 2021, Sinwar had challenged Israel to assassinate him and openly walked the streets of Gaza.

He later did not repeat this procedure, but he was still killed.

Editor's note: This is an updated version of a Profile of Yahya Sinwar published on December 3, 2023.