Isabel de Clare, suo jure 4th Countess of Pembroke and Striguil, was an Anglo-Norman and Irish noblewoman who was the daughter of Aoife MacMurrough and Richard de Clare and one of the wealthiest heiresses in Wales and Ireland. She was the wife of William Marshal, 1st Earl of Pembroke, who served four kings as Marshal of England. Her marriage had been arranged by King Richard I. She ruled Leinster as regent during the absence of her spouse in 1200–1203 and in 1207–1208.