William de Mowbray, Surety for the Magna Charta, 3rd Baron by tenure, eldest son, who was of age in 1194. He was early embittered against King John by being compelled by him to surrender the Barony of Front-Beouf (which Henry I had conferred upon his grandfather, Sir Nigel d'Albini) to a descendant of the original owner. This was probably because Mowbray, upon the accession of King John, was tardy in pledging his allegiance, and at length only swore fealty upon condition that the "King should render every man his right." At the outbreak of the Baronial War he was Governor of York Castle, and it is not surprising that he at once sided with the barons against King John, and was one of the most forward of them. He was selected one of the Sureties for the Magna Charta and was a party to the "Covenant for holding the City and Tower of London" and one of those whom the Pope Innocent III excommunicated by name. He died in 1223-4 at his castle in the Isle of Axlholme and was buried in the Abbey of Newburgh in Yorkshire. He married Agnes d'Albini, daughter of William d'Albini.