Ferdinand I, 1503–64, Holy Roman emperor (1558–64), king of Bohemia (1526–64) and of Hungary (1526–64), younger brother of Holy Roman Emperor Charles V. Brought up in Spain, he was expected to succeed his grandfather, Ferdinand II of Aragón, who, instead, made Charles his heir. In 1521, Charles gave him the Austrian duchies of the Hapsburgs. In the same year Ferdinand married Anna, daughter of Uladislaus II, king of Hungary and Bohemia, in fulfillment of a treaty (1515) between his grandfather, Holy Roman Emperor Maximilian I, and Uladislaus II. When Anna's brother Louis II, who succeeded to the thrones of Bohemia and Hungary on his father's death (1516), was killed at the battle of Mohacs (1526), Ferdinand claimed the succession. He was elected king of Bohemia, but in Hungary he met the rival claim of John I (John Zapolya), supported by Sultan Sulayman I. John's claims were inherited by his son John Sigismund (king as John II). The sporadic warfare in Hungary was indecisive, except that Ferdinand had to pay tribute to the sultan for the strip of NW Hungary that he was allowed to keep with the royal title. In Bohemia, Ferdinand laid the groundwork for Hapsburg absolutism by virtually abrogating (1547) the prerogatives of the diet and the towns; he also began the reconversion of the kingdom to Catholicism by calling in the Jesuits. In Germany, Ferdinand increasingly acted as agent of Charles V, who in 1531 had him elected king of the Romans, which insured Ferdinand's succession as Holy Roman emperor. He had to deal with the Peasants' War and with the rebellions stirred up by Ulrich I, dispossessed duke of Württemberg, where Ferdinand was unpopular as governor. Ulrich secured the aid of Philip of Hesse and defeated Ferdinand at Lauffen (1534). Ferdinand was obliged to restore the duchy to Ulrich. In the war against the Protestant Schmalkaldic League (1546–47), Ferdinand was an important figure. Though a devout Catholic, Ferdinand was less committed against the Reformation than Charles V. When Charles's triumph against the league was turned to defeat by the betrayal of Maurice, elector of Saxony, Ferdinand acted as mediator in making the Treaty of Passau (1552), and in 1555 he negotiated a religious truce at Augsburg (see Augsburg, Peace of). Charles had practically surrendered the government of the empire to Ferdinand by 1556, although formal abdication was not complete until 1558. At the end of his reign, Ferdinand still hoped that the reconvened Council of Trent would bring about a union of the churches. He was succeeded by his son, Maximilian II, who had been crowned king of Bohemia (1562) and king of Hungary (1563) and had been elected king of the Romans (1562) before Ferdinand's death.