The King was the disguise of Prissy Parsley.
He looked like Alvin Parsley, in a copy of one of his performing costumes.
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Scooby-Doo (DC Comics)
Prissy dressed up as the King so that she could get other impersonators to stop and give her a monopoly on his image. She was first detected as an impostor because she left a scrap of her costume behind and it was made of polyester (the real Alvin Parsley was allergic to that material). The gang set a trap for her with Scooby-Doo and Shaggy Rogers dressed as Alvin impersonators, which led to her being caught.
- This is a rare case of pure impersonation. Only Shaggy Rogers ever suggested that the King was a ghost.