Prince of Gwynedd in North Wales. In 1258 he proclaimed himself prince of all Wales and four years later formed an alliance with Simon de Montfort, leader of the baronial opposition to Henry III. He later signed a treaty with Henry, which made him chief of the other Welsh princes but recognized Henry as his overlord (1265). His refusal to pay homage to Edward I led the latter to invade and subjugate Wales (1277–84); Llywelyn died in battle after raising a rebellion against Edward’s rule.