Chubbo was a hamster who used to power Sector V's treehouse. According to Numbuh 3, he was one of the smallest, not very bright, but had the biggest heart. It also seems that he tried to act tough, alluding to the same characteristics as Numbuh 4.

In Operation: G.H.O.S.T., Chubbo is deceased, having the funeral progress with all of Sector V in attendance except for Numbuh 4, who never liked hamsters in the first place (due to them stealing his soda in his room). Numbuh 3 seems especially fond of Chubbo, having spoke about his life in clarity and being the most affected by his death.

Chubbo's ghost rises from his grave during the night and leads thousands of other hamster ghosts in the pursuit of kidnapping Numbuh 3 and taking her to the afterlife after she unwittingly wished to take care of all of the deceased hamsters. When she refuses to stay due to taking care of the hamsters in the living world.

The ghost hamsters terrorizes Sector V as they try to retrieve her, but they are finally defeated by the living hamsters, who proceeded to spray them with soda and dumped a soda machine on top of Chubbo's grave. Locking out the entrance to the hamster afterlife.