CONRAD IV. (1228–1254), German king, son of the emperor Frederick II. and Isabella of Brienne, was born at Andria in Apulia on the 26th of April 1228. In 1235 he was made duke of Swabia and in 1237 was chosen king of the Romans, or German king, at Vienna, in place of his half-brother Henry, an election which was subsequently confirmed by the diet at Spires. After spending some time in Italy he returned to Germany and began to take part in the quarrel which had arisen between the emperor and the pope. In 1240 he called an assembly to Eger, where many of the princes declared openly against the pope, and was soon in arms against Siegfried, archbishop of Mainz, the leader of the papal party in Germany. Although defeated near Frankfort in August 1246 by the anti-king, Henry Raspe, landgrave of Thuringia, he obtained help from the towns and from his father-in-law Otto II., duke of Bavaria, and drove Henry Raspe to Thuringia. He was carrying on the struggle against Henry Raspe’s successor, William II., count of Holland, when the emperor died in December 1250, and a few days later Conrad narrowly escaped assassination at Regensburg. Assuming the title of king of Jerusalem and Sicily, he raised an army by pledging his Swabian estates and marched to Italy in 1251, where with the help of his illegitimate half-brother, Manfred, he overran Apulia and took Capua and Naples. He was preparing to return to Germany at the head of a large army when he died at Lavello on the 21st of May 1254. In September 1246 he married Elizabeth (d. 1273), daughter of Otto of Bavaria, by whom he left a son, Conradin, whom he had never seen.
See F. W. Schirrmacher, Die letzten Hohenstaufen (Göttingen, 1871); C. Rodenberg, Innocenz IV. und das Königtum Sicilien, 1245–1254 (Halle, 1892); J. Kempf, Geschichte des deutschen Reiches während des grossen Interregnums (Würzburg, 1893); and E. Winkelmann, Kaiser Friedrich II. (Leipzig, 1889).