Sigismund I of Poland was born on the 1 January 1467 to Casimir IV of Poland and Elizabeth of Austria. He was their fifth son, but the eldest brother Saint Casimir died before Casimir IV, whilst the second brother, Vladislaus, was elected King of Hungary and Bohemia and John and Alexander who had inherited Poland and Lithuania died childless, so in 1506 he became the King of Poland and Grand-Duke of Lithuania.
In 1515 he and Vladislaus betrothed Vladislaus's children Louis II and Anne to the grandchildren of Maxmilian I. In 1521 he went through a war with the Teutonic Order (1519 - 1521) who were angry they have to pay him and Charles and yet only Charles should be paid.
In the year 1525 he did two important things, Albert von Hohenzollern, the Grandmaster of the Teutonic Order and son of his sister Sophia of Poland was given Prussia and he signed an alliance with Frederick I of Denmark. Albert's conversion to the Lutheran faith was supported by the fact that Sigismund accepted it as the spread of these fought began to affect Poland.
In 1543 his nephew called him into war against the Turks, but before he got there Louis was killed in a Battle of Pest, so he sided with Casimir I, but he, himself, was soon maimed dying in 1545 and was succeeded by his son.
He was married to Barbara Zápolya early in his reign, but they had only two daughters:
Barbara died in 1515 and Sigismund remarried Bona Sforza and had more children:
- King Sigismund II of Poland (1520 - 1576)