King Frederick or King Frederik may refer to:
Frederick I of Denmark Frederick II of Denmark Frederick III of Denmark Frederick IV of Denmark Frederick V of Denmark Frederick VI of Denmark Frederick VII of Denmark Frederik VIII of Denmark Frederik IX of Denmark Frederik X of Denmark Frederick I of Sweden Frederick I of Prussia, previously Frederick III, Elector of Brandenburg Frederick the Great (Frederick II of Prussia) Frederick III, German Emperor, and King of Prussia Frederick I of Württemberg (1754–1816) Frederick of Naples Frederick I, Holy Roman Emperor, also King of Italy Frederick II, Holy Roman Emperor, also King Frederick I of Sicily Frederick III, Holy Roman Emperor, also King of Italy Frederick III of Sicily Frederick the Simple Frederick the Fair Frederick V of the Palatinate, also King Frederick I of Bohemia
In addition, a number of kings of Prussia were named Frederick William: Frederick William I of Prussia (1688–1740) Frederick William II of Prussia (1744–1797) Frederick William III of Prussia (1770–1840) Frederick William IV (1795–1861)
In addition, a number of kings of Saxony were named Frederick Augustus: Frederick Augustus I of Saxony (1750–1827) Frederick Augustus II of Saxony (1797–1854) Frederick Augustus III of Saxony (1865–1932)