High Quality Content by WIKIPEDIA articles! Lord Robert Fitzwalter (died 9 December 1235) was the leader of the baronial opposition against King John of England, and one of the twenty-five sureties of the Magna Carta. He was the third Lord Fitzwalter of Dunmow Castle, Essex; and lord of Baynard`s Castle, in London, to which was annexed the hereditary office of castellain and chief banneret of the City of London. Part of the official aristocracy created by Henry I and Henry II, he served John in the wars in Normandy, in which he was taken prisoner by King Philip II of France and forced to pay a heavy ransom.