Fat Mario was the alias of a drunken and delusional man from Brooklyn, New York who followed Gay Luigi through the Mushroom Kingdom in April of 1994, as seen in Hotel Mario. Although merely an overweight, middle-aged man wearing Mario's red clothes, he believed himself to really be Mario and even made attempts to communicate with the "audience", instructing them to read the "enclosed instruction book" if they needed help.
The man's real name is unknown, and he seemed to be obsessed with defeating Bowser and restoring peace to the kingdom. However, it is widely suspected that the note read by Fat Mario in the game's opening cutscene was planted by Gay Luigi, and the entire bizarre quest was actually an elaborate hoax. "Bowser", along with the "Koopalings", were actually paid actors hired by Gay Luigi to pacify Fat Mario through his drunken fantasies and prevent him from doing anything too stupid.