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The Aristocrats, as they're called in Monster Hits, are the group of monsters who sang "Fur" on Sesame Street.
The lead singer is Stuie Monster, and the back-up singers are a different version of Harvey Monster, Maurice Monster, and a lavender Anything Muppet covered in fur.
These three monsters also appear in the songs "Frazzle" (where the fat blue monster resembled Little Chrissy) and "I Want a Monster to Be My Friend."