Bertrand du Guesclin Bertrand du Guesclin ( c . 1320 – 13 July 1380 ) , known as " the Eagle of Brittany " or " the Black Dog of Brocéliande " , was a Breton knight and French military commander during the Hundred Years ' War . He was Constable of France from 1370 to his death . Well known for his Fabian strategy , he took part in six pitched battles and won the four in which he held command . Origins . Bertrand du Guesclin was born at Motte - Broons near Dinan , in Brittany , first - born son of Robert du Guesclin and Jeanne de Malmaines . His date of birth is unknown but is thought to have been sometime in 1320 . His family was of minor Breton nobility , the seigneurs of Broons . Service in Brittany . He initially served Charles of Blois in the Breton War of Succession ( 1341 – 1364 ) . Charles was supported by the French crown , while his rival , Jean de Montfort , was allied with England . Du Guesclin was knighted in 1354 while serving Arnoul d ' Audrehem , after countering a raid by Hugh Calveley on the Castle of Montmuran . In 1356 - 1357 , Du Guesclin successfully defended Rennes against an English siege by Henry of Grosmont , using guerrilla tactics . During the siege , he killed the English knight William Bamborough who had challenged him to a duel . The resistance of du Guesclin helped restore French morale after Poitiers , and du Guesclin came to the attention of the Dauphin Charles . When he became King in 1364 , Charles sent Du Guesclin to deal with Charles II of Navarre , who hoped to claim the Duchy of Burgundy , which Charles hoped to give to his brother , Philip . On 16 May , he met an Anglo - Navarrese army under the command of Jean de Grailly , Captal de Buch at Cocherel and proved his ability in pitched battle by routing the enemy . The victory forced Charles II into a new peace with the French king , and secured Burgundy for Philip . On 29 September 1364 , at the Battle of Auray , the army of Charles of Blois was heavily defeated by John V , Duke of Brittany and the English forces under Sir John Chandos . De Blois was killed in action , ending the pretensions of the Penthievre faction in Brittany . After chivalric resistance , Du Guesclin broke his weapons to signify his surrender . He was captured and ransomed by Charles V for 100 , 000 franc s . Service in Spain . In 1366 , Bertrand convinced the leaders of the " free companies " , who had been pillaging France after the Treaty of Brétigny , to join him in an expedition to Spain to aid Henry of Trastámara against Pedro I . In 1366 , du Guesclin captured many fortresses ( Magallon , Briviesca and finally the capital Burgos ) . But Henry ' s army was defeated in 1367 by Pedro ' s forces , now commanded by Edward , the Black Prince , at Nájera . Du Guesclin was again captured , and again ransomed by Charles V , who considered him invaluable . However , the English army suffered badly in the battle as four English soldiers out of five died during the Castilian Campaign . The Black Prince , affected by dysentery , soon withdrew his support from Pedro . Du Guesclin and Henry of Trastámara renewed the attack , defeating him at the decisive Battle of Montiel ( 1369 ) . After the battle , Pedro fled to the castle at Monteil , from whence he made contact with du Guesclin , whose army were camped outside . Pedro made an arrangement with du Guesclin ; he bribed him to get an escape . Du Guesclin agreed , but also told it to Henry who gave him more money and land promises to lead Pedro to his tent . Once there , after crossed accusations of bastardy the two half - brothers started a fight to death , using daggers because of the narrow space . At a moment when they fought on the floor , Pedro got the upper side and was about to finish Henry . But then Du Guesclin , who had stayed inactive for he was compromised to both , made his final choice . He grabbed Pedro´s ankle and turned him belly - up , thus allowing Henry to stab Pedro to death and gain the throne of Castile . While turning Pedro down , du Guesclin is claimed to have said " " Ni quito ni pongo rey , pero ayudo a mi señor " " ( I neither put nor remove a King , but I help my Master ) , which has since that moment become a common phrase in Spanish , to be used by anyone of lesser rank who does what he is ordered or expected to do , avoiding any concern about the justice or injustice of such action , and declining any responsibility . Bertrand was made Duke of Molina , and the Franco - Castllian alliance was sealed . Constable of France . War with England was renewed in 1369 , and Du Guesclin was recalled from Castile in 1370 by Charles V , who had decided to make him Constable of France , the country ' s chief military leader . By tradition this post was always given to a great nobleman , not to someone like the comparatively low - born Du Guesclin , but Charles needed someone who was an outstanding professional soldier . In practice du Guesclin had continual difficulties in getting aristocratic leaders to serve under him , and the core of his armies were always his personal retinue . He was formally invested with the rank of Constable by the King on 2 October 1370 . He immediately defeated an English army led by Robert Knolles at the Battle of Pontvallain and then reconquered Poitou and Saintonge forcing the Black Prince to leave France . In 1372 , the Franco - Castillan fleet destroyed the English fleet at the Battle of La Rochelle where more than 400 English knights and 8000 soldiers were captured . Master of the Channel , du Guesclin organized destructive raids on the English coasts in retaliation for the English chevauchée s . Du Guesclin pursued the English into Brittany from 1370 to 1374 , and defeated again the English army at the Battle of Chizé in 1373 . He disapproved of the confiscation of Brittany by Charles V in 1378 , and his campaign to make the duchy submit to the king was halfhearted . Death and burial . An able tactician and a loyal and disciplined warrior , Du Guesclin had reconquered much of France from the English when he died of illness at Chateauneuf - de - Randon while on a military expedition in Languedoc in 1380 . He was buried at Saint - Denis in the tomb of the Kings of France . His heart is kept at the basilica of Saint - Sauveur at Dinan . Later reputation . Because of du Guesclin ' s allegiance to France , 20th century Breton nationalists considered him to be a ' traitor ' to Brittany . During World War II , the pro - Nazi Breton Social - National Workers ' Movement destroyed a statue of him in Rennes .