The Duke of Nuts is the ruler of the Duchy of Nuts. In "The Duke," he is falsely accused of turning Princess Bubblegum green and mostly hairless. Princess Bubblegum claims that he's a bad guy, which causes Finn and Jake to chase him. Fortunately, he is actually a kind guy with a secret. He has a rare condition that makes him have a pudding deficiency. This causes him to constantly eat pudding from Princess Bubblegum's pudding pantry, which is why she hates him. Finn tells Princess Bubblegum about the Duke of Nuts' deficiency, but she doesn't believe him. He is shown to have suffered a "pudding overdose" before. His wife is the Duchess of Nuts, who believes that he has gone rancid due to the false accusation. He has a son named Marquis of Nuts, who seems to be willing to do anything to save his father from death. In "Henchman," he is throwing a birthday party for another son known as Second Nut Son. He has an uncommonly high pitched voice for a grown man.
A humanoid which has a head shaped like a walnut. He also wears a late Medieval, European outfit with puffed shoulders and breeches (similar to Finn's lute suit). It has a blue color for a body sky blue for the arms and legs, indigo padding with purple stripes, and a red cape.
- Lisby the Cashew Butler is his butler.
- He appears to be friends with Marceline, although their history has not been revealed.
- The Duke of Nuts has two children.