William FitzGeoffrey de Mandeville, 3rd Earl of Essex
William FitzGeoffrey de Mandeville (died 1227) was the third Earl of Essex of the second creation from either 1219 or 1216 AD. to his death. He was the second son of Geoffrey Fitz Peter and Beatrice de Say and he succeeded his elder brother Geoffrey FitzGeoffrey as earl and inheritor of the Mandeville earldom and barony. His brother had been a Magna Charta Surety and he was also an ardent supporter of the baronial cause. During the barons war he laid siege to Berkhamsted castle in the month of December 1216 AD, attempting to take it from the castellan Waleran the German. Waleran sallied out when de Mandeville was setting up camp and was able to capture a large amount of de Mandeville's Baggage.and Standard (flag). Later, upon the arrival of Louis VIII of France, the castle was captured on December 20th 1216 AD. He must have reconciled with the royal government of Henry III because by 1220 he complained to the royal administration that his market rights in the town of Moretonhampstead were being infringed upon by Hugh de Chaggeford who was the lord of Chagford which held its own market. In the following court case William's lawyer argued