Underdog's nemesis. (Well, there is Riff Raff, but what kind of real threat does he pose?). Simon, evil genius, and his dimwitted assistant are always out to cause mayhem, and if they can get Underdog out of the way (ideally by kidnapping his dear love, Sweet Polly Purebred), so much the better.

Not to be confused with Simon and the Bar Sinisters, a NYC band.