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.
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.