Polish Zygmunt August
born Aug. 1, 1520, Kraków, Pol.
died July 7, 1572, Knyszyn
King of Poland (1548–72).
Son of Sigismund I , he was crowned coruler with his father in 1530 and ruled the duchy of Lithuania from 1544. After becoming king of Poland (1548), he supported the Teutonic Order in Livonia against Russia (1559) and by treaty incorporated Livonia into Lithuania (1561). Continued threats by Russia compelled Sigismund to unite the lands attached to the Polish crown, and by the Union of Lublin (1569) he united Poland and Lithuania and their respective dependencies. He died childless, which brought the end of the direct Jagiellon dynasty .