Joan of Flanders, Countess of Montfort

Joan of Flanders (c. 1295 – September 1374) was duchess of Brittany by her marriage to John of Montfort. Much of her life was taken up in defense of the rights of her husband to the duchy, and, later, her son's rights to the duchy, which was challenged by the House of Blois during the War of the Breton Succession. Known for her fiery personality, Joan led Montfort's cause after her husband had been captured by Philip VI of France, and began the fight back. There, she displayed considerable skill as a military leader and gained the respect of her people. Shortly after taking refuge in England, she was confined to Tickhill Castle by order of King Edward III.

Joan was highly praised by the chronicler Jean Froissart for her courage and energy. She may have been an inspiration to Joan of Arc and was a role model to Victorian feminists. Because of her feats of leadership, historian David Hume described her as "the most extraordinary woman of the age".