Okay, I'm aware of two Mayors.
The late Sonny Bono, played Mayor Berkowitz in season 1's Man of Steel Bars. Mayor Berkowitz also existed in the comic books for a time.
In season 4's Leathal Weapon, Nancy Dussault played the Mayor but I'm not sure if she was ever addressed by anything except 'Mayor'.
In season 4's John Doe arc, Fred Willard played President Garner. In the Prankster episode where Lois had only one question she could ask the President, I don't remember if his name was ever given.
Tank (who is mildly embarrassed that he remembers this much)
