Who is Yahya Sinwar, the new leader of Hamas?

The new leader of the militant group Hamas has a brutal reputation and a deep understanding of Israel

Yahya Sinwar, the mastermind behind the Oct. 7 attacks on Israel, has been announced as the new leader of the militant group Hamas.

He rose to the top position after the killing of the previous leader, Ismail Haniyeh, in an explosion in Iran that has been blamed on Israel.

Some things to know about Sinwar:

From refugee camp to Hamas militant

Sinwar was born in 1962 in a refugee camp in the Gaza town of Khan Younis. He was an early member of Hamas, which was formed in 1987. He eventually led the group's security arm, which worked to purge it of spies for Israel.

Israel arrested him in the late 1980s and he admitted to killing 12 suspected collaborators, a role that earned him the nickname “The Butcher of Khan Younis.” He was sentenced to four life terms for offenses that included the killing of two Israeli soldiers.

A prison leader

Sinwar organized strikes in prison to improve working conditions. He also studied Hebrew and Israeli society.

He survived brain cancer in 2008 after being treated by Israeli doctors.

Sinwar was released from prison in 2011 by Prime Minister Benjamin Netanyahu as part of an exchange for an Israeli soldier captured by Hamas in a cross-border raid.

Rise to Gaza power

When Sinwar returned to Gaza, he quickly rose through Hamas' leadership ranks with a reputation for ruthlessness. He is widely believed to be behind the 2016 killing of another top Hamas commander, Mahmoud Ishtewi, in an internal power struggle.

Sinwar became head of Hamas in Gaza, effectively putting him in control of the territory, and worked with Haniyeh to align the group with Iran and its proxies around the region while also building the group's military capabilities.

The October attack on Israel

Sinwar, along with Mohammed Deif, the head of Hamas' armed wing, is believed to have engineered the surprise Oct. 7 attack on Israel.

The attack killed about 1,200 Israelis, mostly civilians, and sparked a war that has killed nearly 40,000 Palestinians in Gaza, according to health authorities there.

Hamas said it launched the attack in retaliation for Israel's treatment of Palestinians and to push the Palestinian cause back onto the world agenda.

Israel said it killed Deif in an attack last month.

Where does this leave Hamas?

Sinwar has been in hiding since the attack and cease-fire negotiators have said it takes days to get messages to him. That makes it hard to believe that he will be able to handle Hamas' day-to-day operations.

Sinwar, with his close ties to Hamas' armed wing, is seen as striking an even more hardline tone than Haniyeh did. And he also had a virtual veto over any cease-fire deal Hamas would have reached with Israel since he controls the Israeli hostages central to such an agreement.

Israel has vowed to kill Sinwar.