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.

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,

Before Israel killed him, Hamas leader Yahya Sinwar hid with six Israeli hostages, one of them a U.S. citizen.