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".
Earl An earl is a member of the nobility. The title is Anglo-Saxon in origin, akin to the Scandinavian form jarl, and meant "chieftain", particularly a chieftain set to rule a territory in a king's stead. In Scandinavia, it became obsolete in the Middle Ages and was replaced by duke ("hertig"/"hertug"/"hertog"). In later medieval Britain, it became the equivalent of the continental count (in England in the earlier period, it was more akin to a duke; in Scotland it assimilated the concept of mormaer). However, earlier in Scandinavia, "jarl" could also mean a sovereign prince. For example, the rulers of several of the petty kingdoms of Norway had the title of "jarl" and in many cases they had no less power than their neighbours who had the title of king. Alternative names for the rank equivalent to "Earl/Count" in the nobility structure are used in other countries, such as the "hakushaku" of the post-restoration Japanese Imperial era.