The Norse had various legends that, in prehistoric kings, Norway or part thereof was ruled by a dog. King Eysteinn of Oppland (a region of Norway) is said to have attacked the city of Nidaros and made his son king of it. The Nidrosians rebelled, killing the son. Eysteinn conquered the territory once again and this time installed a dog named Saurr as king. [Those who know Old Norse may realize the name has an unpleasant meaning]. Saurr continued to reign until killed by wolves.
A variant has Gunnar, a Swedish king, conquer Norway and install a dog as ruler.
The legend is not confined to Norway. A Swedish king named Eadgils imposed a dog as king on the prehistoric Danes.
Does any kind of truth exist behind this fairly widespread legend? It appears in a number of literary sources, but its origin cannot be determined. (We might point out that a dog was recently elected Mayor in Montana).