The Duke of Nuts
The Duke of Nuts is, hence the name, The Duke of the Nut Duchy. He first appears in “The Duke of Nuts”, running away from the candy kingdom. It is later revealed in the episode that Princess Bubblegum hates the Duke, and the Duke of Nuts tells Finn and Jake that he had a rare pudding disability, and eats all of everyone’s puddings in the meetings of Ooo royalty. Finn and Jake tell everyone that it’s not the Duke’s fault by doing a play for Princess Bubblegum. It’s actually unrevealed whether the princess continued to hate the Duke or not.
The Duke of Nuts is seen later on in the series, in “Henchman”, in which Marceline tries to trick Finn into thinking that she is going to lead an army of the dead into the Nut Duchy. Really she’s just going to sing a song for the Duke’s new baby.