Otho IV, a German emperor, born in 1174, died May 19, 1218. He was the son of Henry the Lion, duke of Saxony and Bavaria, and of Matilda, sister of Richard Coeur de Lion. His youth was passed at the court of England. In 1197 the emperor Henry VI. of the house of Hohenstaufen died, and left his crown to his son Frederick II., then an infant. Otho was at that time duke of Saxony, and, supported by the Guelphs, he claimed the imperial throne. His claim was opposed by Philip of Swabia, who had the support of the Ghibellines. A civil war ensued, which ended after eight years by the flight of Otho to England, and Philip held the throne till 1208, when he was assassinated. Otho thereupon returned, was recognized as emperor, and was crowned at Rome by Pope Innocent III. in 1209. The pope made it a condition of this coronation that Otho should relinquish in favor of the church the nomination to certain benefices; but the emperor violated his oath, and was excommunicated by the pope and formally deposed by the German princes. The rightful heir Frederick, then king of Naples and Sicily, was elected in his place.

A second civil war now began, and the alliance of Otho with John, king of England, added to his enemies the king of France, Philip Augustus, by whom he was beaten at the battle of Bovines in 1214. In 1215 he marched against Waldemar, king of Denmark, who had formed a league with Frederick. He captured Hamburg, but a sentence of excommunication having been issued against him, he was no longer able to carry on the Avar, and retired to his hereditary estates in Brunswick. His life was published by Langerfeldt in 1872.