Why is Louis IX also known as Saint Louis?

Louis IX is known as Saint Louis because he was canonized by Pope Boniface VIII in 1297, making him the only king of France to be officially numbered among the saints of the Roman Catholic Church.1

His reputation for sanctity was rooted in his deep personal piety and his commitment to his role as a Christian ruler who felt duty-bound to lead his people toward salvation. During his reign, he earned widespread respect for his fairness, wisdom, and impartiality, often acting as an arbitrator in disputes. He was also known for his concern for the poor and his efforts to ensure justice within his kingdom, such as appointing investigators to correct administrative abuses. Even before his formal canonization, the public held him in such high regard that they prayed at his tomb, viewing him as a holy figure.231