Brunanburh is a city-kingdom in the Seven Kingdoms. Despite the fact that it only includes the city and the immediate lands around it, the size of the city and its importance to the rest of the Seven Kingdoms has elevated it to preeminent status.
It is ruled by a burhealdor, which literally means "fortress-elder," and is generally the equivalent of the Imperial term "mayor." However, the Burhealdor of Brunanburh is accounted not only a king, but the bretwalda, or high king of all the Seven Kingdoms.
It's current burhealdor is Sigeberht Alfredson.