Mr. S. Cooper is the man who owns a carnival whose patrons were being murdered.
Mr. Cooper runs the Cooper Carnival. Previously, he was the lot manager for Bunker Brothers. He gives Sam and Dean a job in his circus. Little did he know that in his circus, the blind man was a monster who dressed up as a clown to get to kids so he can eat their parents.
Upon finding that they are hunting a Rakshasa, the brothers assume that it's Mr. Cooper. While investigating the trailers, Sam checks out Mr. Cooper's, and runs into him. Mr. Cooper promptly considers him a "Peeping Tom". Simultaneously, in the blind man's trailer, Dean discovers the real identity of the rakshasa.