Which Holy Roman Emperor was also known as 'the Debonair'?

Louis I, byname Louis the Pious, or the Debonair, French Louis le Pieux, or le Débonnaire, German Ludwig der Fromme (born April 16, 778, Chasseneuil, near Poitiers, Aquitaine [now in France]—died June 20, 840, Petersau, an island in the Rhine River near Ingelheim [now in Germany]), Carolingian ruler of the Franks who succeeded his father, Charlemagne, as emperor in 814 and whose 26-year reign (the longest of any medieval emperor until Henry IV [1056–1106]) was a central and controversial stage in the Carolingian experiment to fashion a new European society.

Commonly called Louis the Pious, he was known to his contemporaries by the Latin names Hludovicus or Chlodovicus, which echo the Latin name of Clovis (c. 466–511), the illustrious founder of the Merovingian dynasty. Louis was appointed king of Aquitaine in 781 and was already a seasoned 35-year-old politician and military commander when he became coemperor with Charlemagne in 813. He was the fourth monarch of the Carolingian dynasty, preceded by his father; his uncle, Carloman; and his grandfather, Pippin III, the Short.