Charles IX, also Carl (Swedish: Karl IX; 4 October 1550 – 30 October 1611), reigned as King of Sweden from 1604 until 1611. 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 1569.
Both Charles and one of his predecessors, Eric XIV (r. 1560–1569), took their regnal numbers according to a fictitious history of Sweden. He was actually the third Swedish king called Charles.