John III of Brittany

John III the Good (1286–1341), son of Arthur II, became Duke of Brittany in 1312 and ruled through nearly thirty years of peace and prosperity. He was a loyal ally of the French crown: he fought for Philip VI at Cassel in 1328, and in 1340 his fleet was destroyed with the French at Sluys.

Yet as Earl of Richmond from 1334 he had also sworn homage to Edward III, so when the Hundred Years' War began he held land under both kings. He resented his stepmother Yolande and her son John of Montfort, whom he would not accept as heir.

His marriages were childless, and he considered leaving the duchy to the French crown. He died on 30 April 1341, and his death opened the Breton War of Succession.