Robert I of Flanders

Robert I, known as Robert the Frisian, was count of Flanders from 1071 until his death in 1093. He was a son of Count Baldwin V out of his first marriage, He was the older brother of Count Baldwin VI and claimed the countship after defeating his nephew Arnulf III and his allies, which included King Philip I of France, Count Eustace II of Boulogne and the counts of Saint-Pol and Ardres at the Battle of Cassel. He subsequently made peace with Philip, who became his stepson-in-law, but remained hostile to his sister Matilda and her husband William the Conqueror, who was king of England and duke of Normandy.