Hamasâs leader in Gaza is considered an architect of the Oct. 7 attacks that prompted Israel to retaliate. As mediators seek a cease-fire, a deal depends on Mr. Sinwar as well as his Israeli foes.Hamasâs leader in Gaza is considered an architect of the Oct. 7 attacks that prompted Israel to retaliate. As mediators seek a cease-fire, a deal depends on Mr. Sinwar as well as his Israeli foes.