Yahya Sinwar, the Hamas leader who was killed by Israeli forces in the Gaza Strip, was the mastermind behind the Oct. 7 attack on Israel that sparked the war. He rose to the top position in August after the killing of the previous leader,

During his 22 years in Israeli prison, Sinwar was an avid student not only of Hebrew but also of Jewish history, including pogroms. His 2011 release brought another lesson: Sinwar, known at the time as the “Butcher of Khan Yunis” for his brutality in dispatching suspected informers,

Mr. Sinwar, one of the main architects of the Oct. 7 Hamas-led attack on Israel, spent decades with the militant group, working his way to the top of its leadership.