LOUIS IV. (921-954), king of France, surnamed "d'Outremer" (_Transmarinus_), was the son of Charles III. the Simple. In consequence of the imprisonment of his father in 922, his mother Odgiva (Eadgyfu), sister of the English king Æthelstan, fled to England with the young Louis--a circumstance to which he owes his surname. On the death of the usurper Rudolph (Raoul), Ralph of Burgundy, Hugh the Great, count of Paris, and the other nobles between whom France was divided, chose Louis for their king, and the lad was brought over from England and consecrated at Laon on the 19th of June 936. Although his _de facto_ sovereignty was confined to the town of Laon and to some places in the north of France, Louis displayed a zeal beyond his years in procuring the recognition of his authority by his turbulent vassals. The beginning of his reign was marked by a disastrous irruption of the Hungarians into Burgundy and Aquitaine (937). In 939 Louis became involved in a struggle with the emperor Otto the Great on the question of Lorraine, the nobles of which district had sworn an oath of fidelity to the king of France. When Louis married Gerberga, sister of Otto, and widow of Giselbert, duke of Lorraine, there seemed to be a fair prospect of peace; but the war was resumed, Otto supporting the rebel lords of the kingdom of France, and peace was not declared until 942, at the treaty of Visé-sur-Meuse. On the death of William Longsword, duke of Normandy, who had been assassinated by Arnulf, count of Flanders, in December 942, Louis endeavoured to obtain possession of the person of Richard, the young son and heir of the late duke. After an unsuccessful expedition into Normandy, Louis fell into the hands of his adversaries, and was for some time kept prisoner at Rouen (945), and subsequently handed over to Hugh the Great, who only consented to release him on condition that he should surrender Laon. Menaced, however, by Louis' brother-in-law, Otto the Great, and excommunicated by the council of Ingelheim (948), the powerful vassal was forced to make submission and to restore Laon to his sovereign. The last years of the reign were troubled by fresh difficulties with Hugh the Great and also by an irruption of the Hungarians into the south of France. Louis died on the 10th of September 954, and was succeeded by his son Lothair. The chief authority for the reign is the chronicler Flodoard. See also Ph. Lauer, _La Règne de Louis IV d'Outre-Mer_ (Paris, 1900); and A. Heil, _Die politischen Beziehungen zwischen Otto dem Grossen und Ludwig IV. von Frankreich_ (Berlin, 1904). (R. Po.)