Robert Fitzwalter[c] (died 9 December 1235)[a] was one of the leaders of the baronial opposition against King John, and one of the twenty-five sureties of Magna Carta.[4] He was feudal baron of Little Dunmow, Essex[5] and constable of Baynard's Castle, in London, to which was annexed the hereditary office of castellan and chief knight banneret of the City of London.[4] 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.[4]

The First Barons' War (1215–1217) was a civil war in the Kingdom of England in which a group of rebellious major landowners (commonly referred to as barons) led by Robert Fitzwalter waged war against King John of England. The conflict resulted from King John's disastrous wars against King Philip II of France, which led to the collapse of the Angevin Empire, and John's subsequent refusal to accept and abide by Magna Carta, which John had sealed on 15 June 1215.

The Second Barons' War (1264–1267) was a civil war in England between the forces of barons led by Simon de Montfort against the royalist forces of King Henry III, led initially by the king himself and later by his son, the future King Edward I. The barons sought to force the king to rule with a council of barons, rather than through his favourites. The war also involved a series of massacres of Jews by de Montfort's supporters, including his sons Henry and Simon, in attacks aimed at seizing and destroying evidence of baronial debts. To bolster the initial success of his baronial regime, de Montfort sought to broaden the social foundations of parliament by extending the franchise to the commons for the first time. However, after a rule of just over a year, de Montfort was killed by forces loyal to the king at the Battle of Evesham.[1]