Sigismund_II_Augustus For other nobles of the same name, please see Sigismund.Sigismund II Augustus I (, Ruthenian:Żygimont III Awgust I, , ; 1 August 1520 — 7 July 1572) was King of Poland and Grand Duke of Lithuania, the only son of Sigismund I the Old, whom Sigismund II succeeded in 1548. Married three times, the last of the Jagiellons remained childless, and thus the Union of Lublin introduced Elective monarchy.