'Bürgermeister' is the generic term. It can also be a village mayor or a mayor of a union of villages. A city mostly has an "Oberbürgermeister" (Lord mayor) and different mayors.
What case is "der Burgermeister" in? I thought it was accusative, but then it would be "den".
"Der Bürgermeister" is in the nominative case (the same as the subject "wer". He is this person.)