Louis the Pious (778 – 20 June 840), also called the Fair, and the Debonaire, was the King of Aquitaine from 781. He was also King of the Franks and co-Emperor (as Louis I) with his father, Charlemagne, of the Holy Roman Empire from 813.

As the only surviving adult son of Charlemagne and Hildegard, he became the sole ruler of the Franks after his father's death in 814, a position which he held until his death, save for the period 833–34, during which he was deposed.