LOUIS I., Roman emperor (called "der Fromme," also " le Débonnaire "), was born in 778. He succeeded his father Charlemagne in 814, having in the previous year been declared co-regent. At the beginning of his reign he excited high anticipations by the earnestness with which he attacked the abuses that had accumulated during the later years of Charlemagne's sovereignty. The licentiousness which prevailed at court he sternly suppressed ; he punished counts who were proved to have misused their authority; and he sought to reform the manners both of the secular and of the regular clergy. The Saxons and the Frisians, who, although conquered, had never cordially accepted Frankish rule, were conciliated by mild and generous treatment. A period of trouble and confusion, however, was opened in" 817, when Louis, anxious to establish the order of succession, declared his eldest son Lothair his successor, and made him co-regent, granting him Austrasia with the greater part of Germany. The younger sons of Louis, Pippin and Louis, received, the former Aquitania, the latter Bavaria, Bohemia, Carinthia, and the subject Slavonic and Avar territories. This arrangement was resented by Bernard, king of Italy, the emperor's nephew, who forthwith rebelled. He was soon captured, and condemned to the loss of his sight, while his kingdom was transferred to Lothair. After the death of Bernard, the emperor, who was a man of a gentle and sensitive temper, bitterly repented the harsh punishment which he had sanctioned, and, being further depressed by the death of his first wife, he proposed to resign the crown and retire to a monastery. He was induced to abandon this intention, and (in 819) to marry Judith, the beautiful daughter of Count Welf of Bavaria. In 829 he made a new division of the empire in favour of Charles (afterwards Charles the Bald), his son by his second wife. The three brothers, deeply dissatisfied, combined to declare war against him, and at Compiegne he was taken prisoner. The empress Judith was condemned to the cloister for alleged infidelity to her husband, and Louis was virtually deposed. Pippin and the younger Louis, suspecting that Lothair meant to usurp exclusive authority, changed their policy, and at a diet in Nimeguen the emperor was restored. Soon afterwards he provoked fresh disturbance by granting Aquitania, the territory of Pippin, to Charles, and in 833 the army of the three brothers confronted that of their father near Colmar. When Louis was negotiating with Pope Gregory IV., who had crossed the Alps in the hope of restoring peace, his troops were persuaded to desert him, and on the Lügenfeld (" the field of lies ") he was obliged to surrender to his sons. The empress was sent to Italy, her son to the monastery of Prüm, and at Soissons Louis not only abdicated, but made public confession of his sins, a long list of which he read aloud. Again the arrogance of Lothair awoke the distrust of his brothers, and they succeeded in reasserting the rights of the emperor, whose sufferings had excited general sympathy. He went through the ceremony of coronation a second time, and Lothair found it necessary to confine himself to Italy. After the death of Pippin in 838 Louis proposed a scheme by which the whole empire, with the exception of Bavaria, would have been divided between Charles and Lothair, to whom the empress had been reconciled. The younger Louis prepared to oppose this injustice, and he was supported by the people of Aquitania in the interest of Pippin's sons. A diet was summoned at Worms to settle the dispute, but before it met the emperor died on an island in the Rhine near Mainz, on the 20th of June 840. He had capacities which might have made him a great churchman, but as a secular ruler he lacked prudence and vigour, and his mismanagement prepared the way for the destruction of the empire established by his father. His son Lothair I. succeeded to the imperial title.

See Funck, Ludwig der Fromme, 1832 ; and Simson, Jahrbücher des Fränkischen Reiches unter Ludwig dem Frommen, 1874-76.