Doge Malvolio IV was a medieval duke who lived in his palace in Venice, Italy. He appears in a flashback in "A Menace in Venice", an episode of The Scooby-Doo Show.
The doge's family treasure was hidden somewhere underground in Venice.
The Scooby-Doo Show
Mario took advantage of the Ghostly Gondolier legend to steal the four medallions to get to the treasure.