The title Frederick III may refer to:
Frederick III, King of Sicily (self-styled), also known as King Frederick II of Sicily, (1272-1337)
Frederick III, King of the Romans (German King), previously Duke Frederick I of Austria, (1289-1330)
Frederick III the Simple, King of Sicily, (1341-1377)
Frederick III, Holy Roman Emperor, (1415-1493)
Frederick III, Elector of Saxony, (1463-1525)
Frederick III, Elector Palatine, (1515-1576)
Frederick III, Duke of Holstein-Gottorp, (1597-1659)
Frederick III, King of Denmark, (1609-1670)
Frederick III, Elector of Brandenburg, later King Frederick I of Prussia, (1657-1713)
Frederick III, German Emperor, (1831-1888)
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