William de Cantilupe, 1st Baron Cantilupe (1262-1308) of Greasley Castle in Nottinghamshire and of Ravensthorpe Castle in the parish of Boltby, North Yorkshire, was created Baron Cantilupe in 1299 by King Edward I. He was one of the magnates who signed and sealed the Barons' Letter of 1301 to the pope and was present at the Siege of Caerlaverock Castle in Scotland in 1300, when his armorials were blazoned in Norman-French verse in the Caerlaverock Roll.
 He was born in 1262 at Lenton Priory in Nottinghamshire (to which his maternal ancestors the de Greasley family had been benefactors), the son and heir of Sir Nicholas de Cantilupe (d.1266) of Withcall (an ancient Cantilupe possession) in Lincolnshire, Greasley in Nottinghamshire and Ilkeston in Derbyshire, by his wife Eustachia FitzHugh, daughter and heiress of Ralph FitzHugh of Greasley (whose mother was Agnes de Greasley, heiress of Greasley and Ilkeston) and of Middle Claydon in Buckinghamshire. William's father died when he was aged four and was buried in St Mary's Church, Ilkeston where survives his recumbent effigy and chest tomb, showing him as a "lively" cross-legged warrior, often said to be a depiction reserved for crusaders. He displays the arms of Cantilupe of Greasley sculpted on his shield. Within two years his mother remarried, to William de Ros (1254-1310) of Ingmanthorpe in Yorkshire (uncle of William Ros, 1st Baron Ros (d.1316) who married the heiress of  Belvoir Castle) by whom she had further issue.
 William's father (Sir Nicholas de Cantilupe (d.1266)) was the 5th and youngest son of William II de Cantilupe (d.1251), 2nd feudal baron of Eaton Bray in Bedfordshire, steward of the household to King Henry III (whose own father William I de Cantilupe (died 1239) had been steward of the household to King John, father of Henry III). Sir Nicholas's uncle was Walter de Cantilupe (1195-1266), Bishop of Worcester and his elder brother was Thomas de Cantilupe (1220-1282), Chancellor of England, Bishop of Hereford, who was canonised as a saint in 1320. The senior line died out in the male line in 1273 on the death of his first cousin, 22 year-old Sir George de Cantilupe (1251-1273), 4th feudal baron of Eaton Bray, Lord of Abergavenny, who had inherited vast Welsh estates from his mother Eva de Briouze.
 In May 1274 at the age of 12 he accompanied his uncle Thomas de Cantilupe, who would be appointed Bishop of Hereford the following year, to the Second Council of Lyons. On 29 December 1299 he was summoned by writ of King Edward I addressed to Willelmo de Canti Lupo or Cauntelo, by which he was created Baron Cantilupe (properly Cauntelo), a title in the peerage of England. He signed and sealed the Barons' Letter of 1301 to the pope (as Dominus de Ravensthorpe, "lord (of the manor) of Ravensthorpe").
 He was present at the Siege of Caerlaverock Castle in Scotland in 1300, when his armorials, a version of the arms of the senior line differenced by a fess vair (as seen on his surviving 1301 seal), were blazoned in Norman-French verse in the Caerlaverock Roll as follows:
 Translated by Sir Nicholas Harris Nicolas as: "And William de Cantilupe, whom I for this reason praise, that he has at all times lived in honour. He had on a red shield a fess vair, with three fleurs-de-lys of bright gold issuing from leopard's heads".
 He married twice:
 He died in 1308. It has been suggested that the (heavily restored) recumbent stone effigy of a knight in Felixkirk Church, near Ravensthorpe, is his monument, although others believe it to represent John de Walkyngham (d.1284)