The House of Vasa or Wasa was an early modern royal house founded in 1523 in Sweden. Its members ruled the Kingdom of Sweden from 1523 to 1654 and the Polish–Lithuanian Commonwealth from 1587 to 1668; its agnatic line became extinct with the death of King John II Casimir of Poland in 1672.

John III was King of Sweden from 1569 until his death. He was the son of King Gustav I of Sweden and his second wife Margaret Leijonhufvud. He was also, quite autonomously, the Duke of Finland from 1556 to 1563. In 1581 he assumed the title Grand Prince of Finland. He attained the Swedish throne after a rebellion against his half-brother Eric XIV. He is mainly remembered for his attempts to close the gap between the newly established Lutheran Church of Sweden and the Catholic Church, as well as his conflict with and murder of his brother.