Butters has been in the show since the beginning. He was later adopted by Stan, Kyle and Cartman as their 4th friend when Kenny died permanently. Later, Kyle, Stan and Cartman decided that they didn't like Butters very much and chose Tweek to "fill the void" instead.
Butters was often referred to as "a little pussy" and the boys got him to do everything for them - often getting Butters grounded in the process.
Butters was the first to mature and give a "semen sample".
Butters' secret alias is Professor Chaos - an evil villain he became when the boys dumped him. He spreads chaos with his sidekick and his hamsters (his "minions"). Some of his evil plots include trying to flood the world with his garden hose and destroying the ozone layer with aerosol spray.
Butters has a tuft of yellow hair, and wears a light blue jacket with green pants.