Born around 1200, likely in Valenciennes to Count Baldwin of Flanders and Hainaut and Marie of Champagne. Died on December 5, 1244 in the Abbey of Marquette, a monastery she founded in a town she fought for. After the false Baldwin was unmasked, Joan forced the French king to release her husband by petitioning for an annulment and making overtures to an anti-French power. They ruled together until his death and when she remarried, it was to a husband who supported her but was largely absent. In addition to expanding the power of towns and religious institutions for women, she was a patron of authors with several books written to her and the first novels in Dutch written during her reign.
For more on Joan, check out her letters on Epistolae