Sigismund II Augustus

Sigismund II Augustus was the only son of Sigismund I the Old and Bona Sforza to survive infancy, groomed from birth to inherit. Crowned co-ruler in 1529 while his father still lived, he succeeded fully in 1548. His first wife, Elizabeth of Austria, died at eighteen in 1545. He then married his mistress Barbara Radziwiłł over his mother's fury and the nobility's opposition - she died five months after coronation. A third marriage to Catherine of Austria also produced no surviving heirs. He maintained peace with neighbors save for the Northern Seven Years' War over Baltic trade, built Poland's first navy and postal service, and patronized a cultural flowering. In 1569 he oversaw the Union of Lublin, merging Poland and Lithuania into the Commonwealth. With his death in 1572 and his sister Anna's in 1596, the Jagiellonian line ended.