Bertrand Du Guesclin (bĕrträN´ dü gĕklăN´), c.1320–80, constable of France (1370–80), greatest French soldier of his time. A Breton, he initially served Charles of Blois in the War of the Breton Succession. Charles was supported by the French crown, while his rival was allied with England. In 1356–57, Du Guesclin held Rennes against English attack. Entering the service of King Charles V of France on Charles's accession (1364), he won the brilliant victory of Cocherel over the forces of King Charles II of Navarre. The victory forced Charles II into a new peace with the French king. Du Guesclin was captured in the same year at Auray by English forces under Sir John Chandos. Ransomed by Charles V, who placed him at the head of the "free companies," the marauding soldiers who pillaged France after the Treaty of Brétigny between France and England, Du Guesclin was sent to Spain to aid Henry of Trastamara (later Henry II of Castile) against Peter the Cruel. Du Guesclin, though successful in the campaign of 1366, was defeated and captured (1367) by Peter and Edward the Black Prince at Nájera. In 1369, however, he and Henry won the battle of Montiel, gaining for Henry the throne of Castile. Warfare with England was renewed in 1369, and Du Guesclin reconquered Poitou and Saintonge and pursued (1370–74) the English into Brittany. He disapproved of the confiscation (1378) of Brittany by Charles V, and his campaign to make the duchy submit to the king was halfhearted. An able tactician and a loyal and disciplined warrior, Du Guesclin had reconquered much of France from the English when he died while on a military expedition in Languedoc.

See biographies by D. F. Jamison (1864), E. V. Stoddard (1897), and R. Vercel (tr. 1934).

Bertrand Du Guesclin: see Du Guesclin, Bertrand.