Louis IV or Louis the Bavarian, 1287?–1347, Holy Roman emperor (1328–47) and German king (1314–47), duke of Upper Bavaria. After the death of Holy Roman Emperor Henry VII the Luxemburg party among the electors set aside Henry's son, John of Luxemburg, because of his youth and chose Louis as rival king to Frederick the Fair. The popes Clement V and his successor John XXII refused to approve Louis's election and, claiming that the imperial throne was vacant, declared the Holy Roman Empire to be under papal rule. This doctrine fitted in well with the papacy's ambition to restore papal authority in Italy. In 1322, Louis defeated and captured Frederick at Mühldorf. Despite this victory, John XXII refused to ratify Louis's election and in 1324 excommunicated him. In 1327–30 Louis was in Italy, where he was crowned emperor by the representatives of the Roman people, and set up Pietro Rainalducci as Antipope Nicholas V. Rainalducci was soon reconciled with the pope, however, and Louis unsuccessfully attempted to reach a settlement. The failure of protracted negotiations with the papacy led (1338) to the declaration at Rhense by six electors to the effect that election by all or the majority of the electors automatically conferred the royal title and rule over the empire, without papal confirmation. Throughout his reign Louis kept adding to the possessions of his family, the house of Wittelsbach. He conferred Brandenburg on his son and added Lower Bavaria to Upper Bavaria. In 1342 he acquired Tyrol by voiding the first marriage of Margaret Maultasch and marrying her to his own son, thus alienating the house of Luxemburg. In 1346 he further antagonized the lay princes by conferring Holland, Zeeland, and Friesland upon his wife. Meanwhile, the pope, Clement VI, took advantage of the hostility to Louis and deposed him (1346), securing the election of a new German king, Charles of Luxemburg (later Holy Roman Emperor Charles IV). Louis was successfully resisting his rival when he was killed in a hunting accident. The controversy between Louis and the popes caused the publication of many books and pamphlets, notably the Defensor pacis by Marsilius of Padua, which supported Louis's claims. William of Occam was another of his supporters.

Louis IV or Louis d'Outremer (lwē dōōtrəmĕr´) [Fr.,=Louis from overseas], 921–54, French king (936–54), son of King Charles III (Charles the Simple). He spent his youth as an exile in England, but at the death of King Raoul he was recalled by the nobles under the leadership of Hugh the Great. However, Louis's energy and independence displeased Hugh, who fought against him with the German king, Otto I, until 942. Captured by the Normans (945), Louis was surrendered to Hugh, by whom he was released only on the cession of Laon (946). Now in alliance with Otto, Louis made war on Hugh and received his submission in 950. Louis was succeeded by his son Lothair.