Arthur III, Duke of Brittany

Arthur III (Breton: Arzhur), more commonly known as Arthur de Richemont (24 August 1393 – 26 December 1458), was briefly Duke of Brittany from 1457 until his death. He is noted primarily, however, for his role as a leading military commander during the Hundred Years' War. Although Richemont briefly sided with the English once, he otherwise remained firmly committed to the House of Valois. He fought alongside Joan of Arc, and was appointed Constable of France. His military and administrative reforms in the French state were an important factor in assuring the final defeat of the English in the Hundred Years' War.

The name Richemont reflects the fact that he inherited the English title of Earl of Richmond, which was held by previous dukes of Brittany, but his tenure was never recognized by the English crown. At the very end of his life he became Duke of Brittany and Count of Montfort after inheriting those titles upon the death of his nephew Peter II. Richemont had no legitimate issue and was succeeded in the duchy by his other nephew, Francis II.