Louis IX was a reformer and developed French royal justice, in which the king was the supreme judge to whom anyone could appeal to seek the amendment of a judgment. He banned trials by ordeal, tried to prevent the private wars that were plaguing the country, and introduced the presumption of innocence in criminal procedure. To enforce the application of this new legal system, Louis IX created provosts and bailiffs.
Following a vow he made after a serious illness and confirmed after a miraculous cure, Louis IX took an active part in the Seventh and Eighth Crusades. He died from dysentery during the latter crusade, and was succeeded by his son Philip III.
Much of what is known of Louis's life comes from Jean de Joinville's famous Life of Saint Louis. Joinville was a close friend, confidant, and counselor to the king, and he also participated as a witness in the papal inquest into Louis' life that ended with his canonisation in 1297 by Pope Boniface VIII.
Two other important biographies were written by the king's confessor, Geoffrey of Beaulieu, and his chaplain, William of Chartres. While several individuals wrote biographies in the decades following the king's death, only Jean of Joinville, Geoffrey of Beaulieu, and William of Chartres wrote from personal knowledge of the king, and all three are biased favorably to the king. The fourth important source of information is
William of Saint-Parthus' 19th century biography, which he wrote using the papal inquest mentioned above.