Sigismund III Vasa was a king who ruled over both Poland and Sweden in the late 16th and early 17th centuries. Born in 1566, he was the son of King John III of Sweden and Catherine Jagellon. His reign in Poland began in 1587, and he became the king of Sweden in 1592, although he faced challenges in maintaining control over both crowns. His rule was marked by conflicts, including the Polish-Swedish War, as he sought to strengthen the Polish-Lithuanian Commonwealth. Sigismund was known for his efforts to promote Catholicism in a predominantly Protestant region, which led to tensions and political strife. He died in 1632, leaving a complex legacy in both nations.