Eustace the Monk Eustace the Monk ( ; c . 1170 – 24 August 1217 ) , born Eustace Busket , was a mercenary and pirate , in the tradition of medieval outlaws . The birthplace of Eustace was not far from Boulogne . A 1243 document mentions a Guillaume le Moine , seigneur de Course , which indicates that the family lived in that vicinity . Life . Early life . Eustace was born a younger son of Baudoin Busket , a lord of the county of Boulogne . According to his biography , he went to Toledo , Spain , and studied black magic there . The author of the " Histoire des Ducs de Normandie " wrote in Eustace ' s own day , " No one would believe the marvels he accomplished , nor those which happened to him many times . " He later returned home to become a Benedictine monk at St Samer Abbey near Calais , and then left the monastery to avenge his murdered father . Other evidence , however , suggests that his father ' s death occurred soon after 1190 . That evidence proves that by 1202 , Eustace was the seneschal and bailiff of the count of Boulogne , Renaud de Dammartin , and that in c . 1204 , the two quarrelled and , accused of mishandling his stewardship , he fled and was declared an outlaw . Renaud confiscated his lands and fields ; Eustace burned two mills in retaliation . Serving England . Eustace became a pirate in the English Channel and the Strait of Dover , both for his own purposes and as a mercenary of France and England . King John of England employed him intermittently from 1205 to 1212 , against Philip II of France . The biography asserts that John gave him command of thirty ships at the start of this assignment . This employment involved Eustace and his brothers raiding the Normandy coast and establishing bases in the Channel Islands ( he and his men held Castle Cornet in Guernsey for a considerable period ) . He took the island of Sark in 1205 . When he raided English coastal villages , King John briefly outlawed him , but soon afterwards issued a pardon because he needed Eustace ' s services . Serving France . However , Eustace switched sides in 1212 ( the biography puts it down to Eustace ' s enemy Renaud de Dammartin allying himself with John and poisoning John ' s mind against Eustace ) and raided Folkestone when English troops seized his Channel Island bases . When civil war broke out in England in 1215 , he supported the rebel barons and ferried Prince Louis of France across the Channel to help them in 1216 . In August 1217 , whilst ferrying much - needed reinforcements to Louis , Eustace met an English fleet under Hubert de Burgh sailing out of Dover . In the ensuing Battle of Dover , Eustace wrought havoc among his former allies , until the English blinded the French with powdered lime . English troops boarded his ships and defeated his men in mêlée . Eustace , his flagship and some other ships managed to escape , but his ship was surrounded on 24 August 1217 in the Battle of Sandwich by Philip d ' Aubigny ' s English fleet of Cinque Ports ships . Eustace was found hiding in the ship ' s bilge s and offered huge sums for his life , which his captors refused , since he had made himself so hated by the English crews . Instead , they allowed him merely the choice between the ship ' s rail or the side of the trebuchet ( carried as deck - cargo to England ) as his execution site . ( Matthew Paris includes the beheading but does not specify which he chose . ) His brothers survived , and continued to hold his Channel Islands base . Aftermath . In June 1217 , during the negotiations for what would be known as the Treaty of Lambeth , the English demanded the return of the Channel Islands from Eustace ' s control , forcibly if necessary . He , however , was killed at sea in August 1217 while negotiations were still ongoing . From then on the negotiations concerned Eustace ' s brothers , with the same demand . The treaty eventually compelled Louis not only to give up his claim to the English throne but to eject Eustace ' s brothers from the Channel Islands . Biography . A romance biography was written on him between 1223 and 1284 by an unknown poet from Picardy , mainly interested in his year or so of adventures after leaving Renaud ' s service . From a forest hideout , this account tells of Eustace duping , ambushing and humiliating Renaud again and again , in different disguises and often stealing his horses . It is linked to the medieval myths of Robin Hood and the 13th century Old French romance " Fouke le Fitz Waryn " on the life of Fulk FitzWarin . This account is then supplemented from 1205 onwards by English government records .