John V, sometimes numbered as VI, bynamed John the Wise, was Duke of Brittany and Count of Montfort from 1399 to his death. His rule coincided with the height of the Hundred Years' War between England and France. John's reversals in that conflict, as well as in other internal struggles in France, served to strengthen his duchy and to maintain its independence.
His alternative regnal name, John VI, as he is known traditionally in old English sources, comes from English partisan accounting as to who was the rightful duke of Brittany during the War of the Breton Succession, which had preceded the rule of his father. Although he faced problems which had lingered from it, his rule as duke was mostly unchallenged. Without significant internal and foreign threats, John V reinforced ducal authority, reformed the military, constructed a coherent method of taxation, and established diplomatic and trade contacts with most of Western Europe.
John V was also a patron of the arts and the Church, and funded the construction of several cathedrals. He is known for creating the "Lycée Lesage" in Vannes.