Charles X Gustav also Carl Gustav, Swedish: Karl X Gustav (November 18, 622 –February 13, 1660) is King of Sweden from 1654 until his death.

He is the son of John Casimir, Count Palatine of Zweibrücken-Kleeburg and Catharina of Sweden.

After his father's death he also succeeds him as Pfalzgraf.

He is married to Hedwig Eleonora of Holstein-Gottorp, who bears his son and successor, Charles XI.

Charles X Gustav is the second Wittelsbach king of Sweden after the childless king Christopher of Bavaria (1441–1448) and he is the first king of the Swedish Caroline era, which has its peak during the end of the reign of his son, Charles XI.

By his predecessor Christina, he is considered de facto Duke of Eyland (Öland) before ascending to the Swedish throne.

His numbering as Charles X derives from a 16th century invention.

The Swedish king Charles IX (1604-1611) chose his numeral after studying a fictitious History of Sweden.

This king was the fourth actual King Charles, but has never been called Charles IV.