John Wayne Gacy ( March 17 1942 -- May 10 1994 ) also known as The Killer Clown , was an American serial killer . John Wayne Gacy , Jr. ( March 17 , 1942 â `` May 10 , 1994 ) was an American serial killer also known as the Killer Clown who committed the rape and murder of 33 teenage boys and young men between 1972 and 1978 .