Why was Frederick I only called "King of Denmark" while Christian III was named "King of Denmark and Norway"?
Frederick I of Denmark Frederick I (7 October 1471 – 10 April 1533) was the King of Denmark and Norway. His name is also spelled "Friedrich" in German, "Frederik" in Danish and Norwegian and "Fredrik" in Swedish. He was the penultimate Roman Catholic monarch to reign over Denmark, when subsequent monarchs embraced Lutheranism after the Protestant Reformation. As King of Norway, Frederick is most remarkable in never having visited the country and was never being crowned King of Norway. Therefore he was styled "King of Denmark, the Vends and the Goths, elected King of 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).