John III (Swedish: Johan III, Finnish: Juhana III; 20 December 1537 – 17 November 1592) 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 ruler of Finland, as Duke John from 1556 to 1563. In 1581 he assumed also 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.
His first wife was Catherine Jagellonica of the Polish-Lithuanian ruling family, and their son Sigismund eventually ascended both the Polish-Lithuanian and Swedish thrones.
More information: https://en.wikipedia.org/wiki/John_III_of_Sweden
King of Sweden
Grand Duke of Finland:
January 1569 – 17 November 1592
10 July 1569
20 December 1537, Stegeborg Castle
17 November 1592 (aged 54), Tre Kronor castle
1 February 1594, Uppsala Cathedral
(m. 1562; died 1583)
Sigismund III, King of Poland and Sweden
Anna, Starosta of Brodnica and Golub
John, Duke of Östergötland
Sophia, Baroness de la Gardie (ill.)
Gustav I of Sweden
mediating between Lutheranism and Catholicism
Catherine Jagiellon (Swedish: Katarina Jagellonica, Lithuanian: Kotryna Jogailatė; 1 November 1526 – 16 September 1583) was a Polish princess and Queen of Sweden as the first wife of King John III. As such, she was also Duchess of Finland (1562–1583) and Grand Princess of Finland (1581–1583). Catherine had significant influence over state affairs during the reign of her spouse and negotiated with the pope to introduce a counter-reformation in Sweden. She was the mother of the future Sigismund III Vasa, King of Poland.
More information: https://en.wikipedia.org/wiki/Catherine_Jagiellon
Gunilla Bielke; Swedish: Gunilla Johansdotter Bielke af Åkerö (25 June 1568 – 19 July 1597) was Queen of Sweden as the second wife of King John III. Queen Gunilla is acknowledged to have acted as the political adviser to John III and to have influenced his religious policies in favor of Protestantism.
More information: https://en.wikipedia.org/wiki/Gunilla_Bielke