John I Albert in the context of "Sigismund I of Poland"

Sigismund I the Old (Polish: Zygmunt I Stary, Lithuanian: Žygimantas I Senasis; 1 January 1467 – 1 April 1548) was King of Poland and Grand Duke of Lithuania from 1506 until his death in 1548. Sigismund I was a member of the Jagiellonian dynasty, the son of Casimir IV and younger brother of Kings John I Albert and Alexander I Jagiellon. He was nicknamed "the Old" in later historiography to distinguish him from his son and successor, Sigismund II Augustus. Before ascending to the Polish and Lithuanian thrones, he was Duke of Głogów from 1499, Duke of Opava from 1501, and governor of Silesia from 1504 on behalf of his brother, King Vladislaus II of Bohemia and Hungary.

Sigismund was born in the town of Kozienice in 1467 as the fifth son of Casimir IV and his wife Elizabeth of Austria. He was one of thirteen children and was not expected to assume the throne after his father. Sigismund's eldest brother and rightful heir Vladislaus II instead became the King of Bohemia, Hungary and Croatia as the successor to George of Poděbrady in Bohemia and then to Matthias Corvinus in Hungary, thus temporarily uniting these kingdoms. When Casimir died, the Polish-Lithuanian realm was divided between the remaining two older sons, with John Albert being crowned King of Poland, and Alexander as Grand Duke of Lithuania. Alexander inherited Poland following John Albert's sudden death in 1501. Hence, Sigismund's reign only began when he succeeded Alexander to both titles in 1506 at the age of 39.

Alexander Jagiellon (Polish: Aleksander Jagiellończyk; Lithuanian: Aleksandras Jogailaitis; 5 August 1461 – 19 August 1506) was Grand Duke of Lithuania from 1492 and King of Poland from 1501 until his death in 1506. He was the fourth son of Casimir IV and a member of the Jagiellonian dynasty. Alexander was elected grand duke of Lithuania upon the death of his father and became king of Poland upon the death of his elder brother John I Albert.