Louis IX (25 April 1214 – 25 August 1270), commonly Saint Louis, was King of France from 1226 until his death. He was also styled Louis II, Count of Artois from 1226 to 1237. Born at Poissy, near Paris, he was an eighth-generation descendant of Hugh Capet, and thus a member of the House of Capet, and the son of Louis VIII and Blanche of Castile. He worked with the Parliament of Paris in order to improve the professionalism of his legal administration.

He is the only canonised king of France; consequently, there are many places named after him, most notably St. Louis, Missouri, in the United States, São Luís do Maranhão, Brazil and both the state and city of San Luis Potosí, in Mexico. Saint Louis was also a tertiary of the Order of the Holy Trinity and Captives (known as the Trinitarians).^{[citation needed]} On 11 June 1256, the General Chapter of the Trinitarian Order formally affiliated Louis IX at the famous monastery of Cerfroid, which had been constructed by Felix of Valois north of Paris.