Yahya Sinwar has been called "the butcher from Khan Yunis" and has been described by experts as both brutal and uncompromising.
The 61-year-old Sinwar was the highest leader of the terrorist-stamped group in Gaza since 2017, later the movement's highest leader after Ismael Haniya was killed in an Israeli attack in Tehran in July, and is often pointed out as the one who de facto ruled the movement.
Together with Mohammad Dayf, he is believed to have been the mastermind behind the October 7 attack, which killed around 1,200 Israelis and led to Israel declaring war on Hamas.
Since the war began, Sinwar has been assumed to be hiding somewhere in Gaza's underground tunnel network. Israeli hostages who have been released have said they saw him, but no particularly secure information has been available for many months.
Imprisoned for 23 years
Sinwar was an extremely hard-line leader, and even his own, within militant Palestinian circles, describe him as bloodthirsty and extreme.
Testimonies describe how he, at the end of the 1980s, stabbed to death Palestinians who collaborated with Israel. Something he both admitted to and boasted about, and was later convicted of.
He sat in an Israeli prison for a total of 23 years, where he immediately took on a leadership role, known for his brutality. In 2011, he was released in a highly publicized prisoner exchange.
Radicalized
A high-ranking source within al-Fatah, the secular Palestinian party that governs on the West Bank, believes that Israel's biggest mistake was releasing Sinwar from prison.
As long as he breathes, he rules, and he is a crazy fanatic, the source has said to the newspaper Haaretz.
He also says that Sinwar was radicalized in Israeli prison to such an extent that he genuinely believed he was "the Prophet Muhammad's assistant."
Born in 1962. Grew up in the Gaza city of Khan Yunis, where his parents fled from Ashkelon in present-day Israel when the Jewish state was formed in 1948.
Was arrested by Israel for the first time when he was just 19 years old. Later started Hamas' security group al-Majd, which was to hunt down "traitors" of various kinds.
Was released in the large prisoner exchange in 2011, when Israel got back the kidnapped soldier Gilad Shalit in exchange for over 1,000 Palestinian prisoners.
In an internal Hamas election in 2017, he was elected as the highest leader of Gaza. He is suspected of having, together with military chief Mohammad Dayf, planned the major terrorist attack on October 7, 2023.
