Arthur III (August 24 1393 – December 26 1458), known as the Justicier and as Arthur de Richemont, was as an old man the duke of Brittany, from 1457 to his death. Belonging to the family of Montfort, he was younger son of Duke John V and just a year before his own death succeeded his nephew Peter II as Duke. Arthur was also Earl of Richmond, a fief in England which had belonged to ducal family of Brittany already for some century and more. Of course, Arthur's position in the war did not help him to keep that earldom.

Arthur was an important figure of the French court even before becoming duke of Brittany. He was a reference for his brother Duke John VI the head of the French army (constable of France) in the peak of the Hundred Years War. He was one of the supporters of the charismatic Joan of Arc. Arthur was known by his tenacity and bad temper, characteristics that had them expelled from the court in 1427. However, in 1435, Arthur of Brittany was again an influential man and orchestrated the peace treaty of Arras between Charles VII of France and Philip III, duke of Burgundy.

Arthur was married three times but had no children and was succeeded as Duke of Brittany by his nephew Francis II, count d'Etampes.

See also: Dukes of Brittany family tree