Ottocar II or Přemysl Ottocar II, c.1230–1278, king of Bohemia (1253–78), son and successor of Wenceslaus I. Ottocar shrewdly exploited the disorders of the great interregnum in the Holy Roman Empire to build an empire reaching from Bohemia to the Adriatic. He won (1251) the duchy of Austria by election, marriage, and conquest and became involved in a long war over Styria with Bela IV of Hungary; after defeating (1260) Bela, he added Styria to his possessions and, having procured the annulment of his first marriage, married a Hungarian princess. In 1269 he acquired, through diplomacy, Carinthia, Carniola, and Istria. Thus Ottocar's domains included most of the later Hapsburg crownlands. Ottocar sought the German crown in 1273, but his unprecedented power made him unpopular with the electors. Rudolf I of Hapsburg was elected Holy Roman emperor. Ottocar, who contested the election, was declared deprived of his dominions by the Diet of Regensburg (1274) and was placed by Rudolf under the ban of the empire (1275). In 1276, yielding to a powerful German-Hungarian coalition headed by Rudolf, Ottocar surrendered all but Bohemia and Moravia, with which he was reinvested by Rudolf. However, Ottocar's revived ambitions and Rudolf's interference in Bohemian affairs provoked a new war. Ottocar was defeated and killed on the Marchfeld in a fierce battle against Germans and Hungarians. He was succeeded by his son, Wenceslaus II. Ottocar greatly encouraged the growth and independence of the towns, thereby earning the reproach of favoring the Germans (most numerous in the towns) over the Czechs, and he sought to reduce the power of the great nobles. An astute diplomat, he was also a courageous warrior. He helped to conquer East Prussia from the pagan Prussians and founded the city of Königsberg (now Kaliningrad).