Mayor McCheese is one of the inhabitants of McDonaldland, where Ronald McDonald and all of his friends in McDonald's merchandising live. He was introduced in 1971 along with the Hamburglar, the Grimace, and the Professor in order to fill out the McDonaldland cast.
Although many of the other McDonaldland characters have continued to appear in commercials, most of the administration and government of the area, including the Mayor and Officer Big Mac, have long since disappeared, and can only be found in scattered Playplaces which were built before the Mayor fell out of popularity. With crime in McDonaldland being limited to the exploits of the Hamburglar, this has not changed matters much.
The Mayor disappeared after H.R. Pufnstuf successfully sued McDonald's, claiming that the burger chain had stolen the look and feel of Pufnstuf characters for a number of McDonaldland characters. The claim was even successfully made that McDonald's had hired away several former Pufnstuf employees to help design characters. The eventual outcome of the suit was that several inhabitants of McDonaldland were quietly removed from the lineup, never to be seen again.
There exists a great deal of conspiracy theory online and constant cultural reference to Mayor McCheese. It is unclear why people are so obsessed with the former Mayor, but the fact still remains that he enchants and delights people, both children and adults, to this day.