Filth, introduced in the second book, is a primate-like creature described as "a monkey... with a distinctly human cast to his crooked face".
He is said to have been jester to King Claus of Day until the death of Princess Boa and still lives in the Twilight Palace, where Candy encounters him after her escape from Otto Houlihan on the island of Babilonium.
Filth reveals the history of Princess Boa and the existence of King Claus's Cabinet of Wonders to Candy. He is suggested to believe that Candy is Boa's reincarnation.