Harry the Hypnotist posed as the Ghost Clown.
History
Scooby-Doo, Where Are You!
Season one
He was a circus hypnotist. He dressed up as the Ghost Clown, hypnotizing Shaggy, Scooby, and Daphne to do dangerous acts in Barnstorm's circus, causing mayhem. He went against the circus because he was sent to prison after he was caught stealing at the circus. (Bedlam in the Big Top)