Uncle Donald is one of Mr. Pig's relatives and a guest at Tree Trunks' wedding in the episode "Apple Wedding." He sits on the left side of the aisle with the rest of Mr. Pig's relatives and is among the wedding guests that Princess Bubblegum puts in the Candy Dungeon with the King of Ooo. Mr. Pig mentions him while listing the people he and Tree Trunks care about, along with Finn, Banana Guard #1, Jake, and Jake Jr.
He wears a greenish-black beret and a black suit with a green shirt and bow tie. He is wrinkled from old age, and folds of skin cover his eyes.