William de Mowbray

William de Mowbray 6th Baron of Thirsk 4th Baron Mowbray
Arms of the William de Mowbray
Hereditary
Predecessor	Nigel de Mowbray II, 5th Baron of Thirsk
Successor	Roger de Mowbray II, 7th Baron of Thirsk
Issue Nigel de Mowbrey III Roger de Mowbrey II
Detail Titles and styles 6th Baron of Thirsk 4th Baron Mowbray
Family	Mowbray
Father	Nigel de Mowbray II, 5th Baron Thirsk
Mother	Mabel de Clare
Born	1173 Thirsk Castle, Thirsk, Yorkshire, Kingdom of England
Died	1224 Isle of Axholme, Epworth, Lincolnshire, Kingdom of England
Occupation	Peerage of England

William de Mowbray, 6th Baron of Thirsk, 4th Baron Mowbray (c. 1173–c. 1224) was an Norman Lord and English noble who was one of the twenty five executors of the Magna Carta. He was described as being as small as a dwarf but very generous and valiant.

William was the eldest of the one daughter and three or four sons of Nigel de Mowbray, by Mabel, thought to be daughter of William de Patri, and grandson of Roger de Mowbray.

William appears to have been in the company of Richard I in Speyer, Germany, on 20 November 1193 during Richard's period of captivity on his return from Palestine. In 1194 he had livery of his lands. paying a relief of £100. He was immediately called upon to pay a sum nearly as large as his share of the scutage levied towards Richard's ransom, for the payment of which he was one of the hostages. William was later a witness to Richard's treaty with Baldwin of Flanders in 1197.

In 1215 Mowbray was prominent with other north-country barons in opposing King John. He was appointed one of the twenty-five executors of the Magna Carta, and as such was specially named among those excommunicated by Pope Innocent III. His youngest brother, Roger, has sometimes been reckoned as one of the twenty-five, apparently by confusion with, or as a substitute for, Roger de Mumbezon. Roger died without heirs about 1218, and William received his lands.

In the First Barons' War, Mowbray supported Louis. Mowbray was taken prisoner in the Battle of Lincoln (1217), and his estates bestowed upon William Marshal the younger; but he redeemed them by the surrender of the lordship of Bensted in Surrey to Hubert de Burgh, before the general restoration in September of that year.