Poland-Lithuania
In 1592 Sigismund succeeded his father John III of Sweden to the Swedish throne, but in 1587 he had also been elected king of Poland-Lithuania making him the monarch of both nations. Sigismund, who was a Roman Catholic failed however to gain support in Lutheran Sweden, and was eventually deposed and succeeded by his uncle Charles IX in Sweden 1599.
Read more about this topic: Political Unions Involving Sweden