Treaty of Kraków in the context of "Polish–Teutonic War (1519–21)"

Albert of Prussia (German: Albrecht von Preussen; 17 May 1490 – 20 March 1568) was a German prince who was the 37th grand master of the Teutonic Knights and, after converting to Lutheranism, became the first ruler of the Duchy of Prussia, the secularized state that emerged from the former Monastic State of the Teutonic Knights. Albert was the first European ruler to establish Lutheranism, and thus Protestantism, as the official state religion of his lands. He proved instrumental in the political spread of Protestantism in its early stage, ruling the Prussian lands for nearly six decades (1510–1568).

Albert was great-grandson of the converted pagan ruler Jogaila of Poland and Lithuania, vanquisher of the Teutonic Knights at the Battle of Grunwald. He was also a member of the Brandenburg-Ansbach branch of the House of Hohenzollern. He became grand master of the Teutonic Knights in their attempt to diplomatically win over the Polish-Lithuanian union. His skill in political administration and leadership ultimately succeeded in reversing the decline of the Teutonic Order. But Albert was sympathetic to the demands of Martin Luther, whose teachings had become popular in his lands. So he rebelled against the Roman Catholic Church and the Holy Roman Empire by converting the Teutonic state into a Protestant and hereditary realm, the Duchy of Prussia, for which he paid homage to his uncle, Sigismund I, king of Poland. That arrangement was confirmed by the Treaty of Kraków in 1525. Albert pledged a personal oath to the king and in return was invested with the duchy for himself and his heirs.