Grimby is one of the three individuals that Finn thinks are tart burglars and attacks in the Desert of Doom in "The Other Tarts." He and his compatriots, Taddle and JJ, steal some of the (poisoned) royal tarts from Finn and Jake. They are last seen escaping into the desert and were most likely paralyzed by the tarts.
Grimby is the leader of the three hobos. He is the one who cooks their bean the most. He also lets JJ cook it some, but he apparently does not trust Taddle with it. When he is informed Finn and Jake have the royal tarts, he becomes very excited and rallies the group into trying to steal them. It is unclear how much he cares about his compatriots; as soon as Finn and Jake attack, he eats their bean himself.
Grimby is a light gray, semi-blue color. He is completely bald, aside from a few stubbly hairs on the back of his head and shoulders. He has an elongated face and nose, with no visible nostrils. He wears brown pants, the legs of which are tucked into his grayish-brown boots with light-brown cuffs and soles. A single piece of rope/string is tied around his left boot.
He wears a futuristic hydration system that consists of a pack on his back and two casings on his chest.
Hush. *Blows on the bean* I ain't gon' burn it.