Sigismund II Augustus (Polish: Zygmunt II August, Lithuanian: Žygimantas Augustas; 1 August 1520 – 7 July 1572) was King of Poland and Grand Duke of Lithuania, the son of Sigismund I the Old, whom Sigismund II succeeded in 1548. He was the first ruler of the Polish–Lithuanian Commonwealth and the last male monarch from the Jagiellonian dynasty.
Sigismund was elder of two sons of Italian-born Bona Sforza and Sigismund the Old, and the only one to survive infancy. From the beginning he was groomed and extensively educated as a successor. In 1529 he was chosen as king in vivente rege election while his father was still alive. Sigismund Augustus continued a tolerance policy towards minorities and maintained peaceful relations with neighbouring countries, with the exception of the Northern Seven Years' War which aimed to secure Baltic trade. Under his patronage, culture flourished in Poland; he was a collector of tapestries from the Low Countries and collected military memorabilia as well as swords, armours and jewellery. Sigismund Augustus' rule is widely considered as the apex of the Polish Golden Age; he established the first regular Polish navy and the first regular postal service in Poland, known today as Poczta Polska. In 1569, he oversaw the signing of the Union of Lublin between Poland and the Grand Duchy of Lithuania, which formed the Polish–Lithuanian Commonwealth and introduced an elective monarchy.