Why was Frederick I only called "King of Denmark" while Christian III was named "King of Denmark and Norway"?
Election of Christian III The election of Christian III as king of Denmark and Norway on 4 July 1534 was a landmark event for all of Denmark and Norway. It took place in the church in the town of Rye, eastern Jutland, where the Jutlandic nobility elected Prince Christian, son of King Frederick I and Duke of Schleswig and Holsten, as king. This brought about the Count's Feud ("Grevens Fejde") and later also led to the implementation of the Protestant Reformation in Denmark and Norway.
Frederick Augustus I of Saxony Frederick Augustus I (full name: "Frederick Augustus Joseph Maria Anthony John Nepomuk Aloysius Xavier"; German: "Friedrich August Josef Maria Anton Johann Nepomuk Alois Xavier" ; Polish: "Fryderyk August Józef Maria Antoni Jan Nepomucen Alojzy Ksawery Wettyn" ; 23 December 1750 – 5 May 1827) was King of Saxony (1805–1827) from the House of Wettin. He was also Elector Frederick Augustus III ("Friedrich August III.") of Saxony (1763–1806) and Duke Frederick Augustus I (Polish: "Fryderyk August I" ) of Warsaw (1807–1813).