Mr. Mayor is a character from the LEGO Friends episodes. He is yet to appear in any sets.
Mr. Mayor is the mayor of Heartlake City. In Getting out the Vote, on his Campaign Posters, his real name is revealed to be Oliver but it never mentioned his last name.
Since Mayor Butaire is Mayor in the Netflix series it can be assumed Mr. Mayor lost the elections.
This is supported by the former Mayor throwing a crumpled up paper ball at Mayor Butaire, most likely because he is angry at being replaced/voted out.
He spends the rest of the episode avoiding the bodyguard, who is looking for the thrower while taking down his Campaign Posters.