From Sonic Retro
The Marxio Brothers (Grouchio, Chicio and Harpio) were three characters based two on sources, the Marx Brothers and both Mario and Luigi, from the Super Mario Bros. franchise. They were three electricians who fled their original world, the Marxio World, because they were terrified of it, another obvious poke at the Nintendo franchise.
The brothers found themselves employed by Doctor Robotnik on multiple occasions, setting themselves up for antagonistic confrontations with Sonic and Knuckles. A multi-part Knuckles story saw them installed as the overseers of Carnival Night Zone; Knuckles eventually dealt with the brothers by punching a fault line to detatch the entire zone from the Floating Island.