Catherine Jagiellon, queen of John III of Sweden (born 1526)

Catherine Jagiellon was a princess of the Polish–Lithuanian Commonwealth and Queen of Sweden from 1569 as the wife of King John III. Catherine had significant influence over state affairs during the reign of her spouse. She negotiated with the pope to introduce Counter-Reformation in Sweden. She was the mother of Sigismund III Vasa.

John III was King of Sweden from 1569 until his death. He attained the Swedish throne after a rebellion against his half-brother Erik 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 possible murder of his brother.