Charles IX of Sweden (d. 1611)
Charles IX, also Carl (Swedish: Karl IX; 4 October 1550 – 30 October 1611), reigned as King of Sweden from 1604 until his death. He was the youngest son of King Gustav I (r. 1523–1560) and of his second wife, Margaret Leijonhufvud, the brother of King Eric XIV and of King John III, and the uncle of Sigismund, who became king both of Sweden and of Poland. By his father's will Charles received, by way of appanage, the Duchy of Södermanland, which included the provinces of Närke and Värmland; but he did not come into actual possession of them till after the fall of Eric and the succession to the throne of John in 1568.

Both Charles and one of his predecessors, Eric XIV (r. 1560–1568), took their regnal numbers according to a fictitious history of Sweden. He was actually the third Swedish king called Charles.

He came into the throne by championing the Protestant cause during the increasingly tense times of religious strife between competing sects of Christianity. Just under a decade after his death, these would re-ignite in the Thirty Years' War of 1618-1648. These conflicts had already caused the dynastic squabble rooted in religious freedom that deposed Charles' nephew (Sigismund III) and brought Charles to rule as king of Sweden.

His reign marked the start of the final chapter (dated 1648 by some) both of the Reformation and of the Counter-Reformation. With the death of his brother John III of Sweden in November 1592, the Swedish throne went to his nephew, the Habsburg ally Sigismund of Poland and Sweden. During these tense political times, Charles viewed the inheritance of the throne of Protestant Sweden by his devout Roman-Catholic nephew with alarm. Several years of religious controversy and discord followed.

While King Sigismund resided in Poland, Charles and the Swedish privy council ruled in Sigismund's name. After various preliminaries, the Riksdag of the Estates forced Sigismund to abdicate the throne to Charles IX in 1595. This eventually kicked off nearly seven decades of sporadic warfare as the two lines of the divided House of Vasa both continued to attempt to remake the union between the Polish and Swedish thrones with opposing counter-claims and dynastic wars.

Quite likely, the dynastic outcome between the Swedish and Polish representatives of the House of Vasa exacerbated and radicalized the later actions of Europe's Catholic princes in the German states such as the Edict of Restitution of 1629. In fact, it worsened European politics to the abandonment or prevention of settling events by diplomacy and compromise during the vast bloodletting of the Thirty Years' War.