Crayon Boy is a member of the Gallagher Safety Patrol who was fed up with letting the other students cut in front of him in the lunch line; leaving him with nothing left to eat when he reached the front of the line. He pretends to have psychic powers and "predicts" that other students are about to commit crimes. After Numbuh and Numbuh 4 were arrested, Numbuh 3 was the detective solving the mysteries of the case Crayon Boy was seen working with the Delightful Children From Down the Lane, but they were soon arrested for running in the halls. He had also cut a deal with Joe Balooka and had Kuki then Joe arrested by the Hall Squad. Crayon Boy then had the Hall Squad arrest themselves. This in turn made him the only kid not in detention during lunch time. His plan succeeds, but when he asks for fifty pizza bagels, the cafeteria lady tells him that they are next week's lunch, and they are currently serving lima bean sandwiches. A sandwich is then ploped onto his tray shortly after finding after. He then rips the sandwich to pieces before crying over still not getting any pizza bagels.
He is perhaps the only villain in the show who has never faced defeat by the KND, making him the most successful villain to date of having never been punished. However while he succeeded in getting the other kids in detention so he could be the first in line in lunch, he did not succeed in getting his desired pizza bagels as that was next week's lunch.
He has an uncanny resemblance to Sideshow Bob from The Simpsons and seems to have Heterochromia, meaning his eyes have different colors. He is voiced by Richard Horvitz.
His pretended psychic future drawing abilities appear to be based off the character Isaac Mendez from the NBC show Heroes as his pupils disappear when he draws out the future which is similar to what happens to Isaac when he paints the future out.
Crayon Boy appears in the KND comic "Operation: T.R.A.D.E.", revealing that his name is Oliver. He buys everyone's lunches using faux Yipper Cards trying to trade for one of Numbuh 3's pizza bagels, which are later revealed to just be pretend food.