Blanche of Castile (1188-1252) was the wife of King Louis VIII of France and the mother of King Louis IX. As a great-granddaughter of Henry II of England, she had a claim to the English throne, and this was used in her husband's attempt to invade England. Blanche organized troops in the Calais area for this attempt. She also supported the war against the Cathar sect of Christianity in southern France, being a pious woman; bibles and psalters she commissioned still survive. This earned her the support of the Roman Catholic Church, which would help her hold the country together in future years.

When her husband died in 1226, she became regent for her son until he reached adulthood in 1234. During this time she repelled Henry III of England's 1230 attempt to take back former English lands in France, and kept the French lords from gaining more power than the royal throne. Riding at the head of her troops, dressed in white and on a white horse, she must have been an interesting sight. Her power did not stop student revolts in Paris, but she did bring more territory under the sway of the French crown through treaties and marrying relations to their rulers.

Louis IX kept her as an advisor, and in 1247 when he decided (much against Blanche's will) to go on crusade to the Holy Land, he left Blanche as regent and caretaker of his children. She again increased the territory of France through treaties, and suppressed rebellions, despite the heavy tax burden necessary to support the crusade. She even negotiated Louis' release when he was captured at the battle of El Mansurah. Another son, Alphonse, helped her toward the end of her life, and she died in the Louvre in 1252.

Her piety is thought to have been a great influence on her son, who became St. Louis. She also wrote troubadour-style songs which have survived the years, such as "Amours, u trop tart me sui pris," still recorded by those specializing in medieval music.