Guillermo is a character that only appeared in "Uncle Grandpa for a Day". His bike was accidentally crushed by The UG RV, and because Uncle Grandpa and Belly Bag had jars of peanut butter stuck on their heads, it was up to Mr. Gus and Pizza Steve to help out Guillermo. He is voiced by Eric Bauza
Guillermo has black hair slicked up into a pompadour with gel. He has light tan skin and wears an orange polo shirt, blue jeans, and black shoes.
Guillermo is a gullible little boy. He is quick to believe the things that are told to him (like believing the garbage can actually was a magical Uncle Grandpa bike because Pizza Steve told him so and did all of these bogus things without him actually riding the "bike" himself and ends up taking the "bike" to Danger Mountain believing he could actually ride down it). He is also an enthusiastic boy, being pumped and excited when Pizza Steve and Mr. Gus show him how to use the "magical Uncle Grandpa" bike.