There are several monsters in Rick Riordan’s book Percy Jackson and the Olympians: The Lightning Thief that were not featured in the movie version. One of these is Argus, the security guard with one hundred eyes. Argus’s eyes are spread all around his body so he can see in many different directions at one time. He is the head of camp security and he gives Percy, Annabeth, and Grover a ride to the Greyhound bus stop on the Upper East Side in New York City.

Another character missing from the film is Procrustes, also known as Crusty, who owns the bed store. When Percy, Grover, and Annabeth duck into the store for safety, Procrustes lures them into a trap on his beds, and Percy ends up having to slay him.

Cerberus, the three-headed dog, is also a notable monster who is missing from the film adaptation of the story. Cerberus is guarding the gate to the underworld when Percy, Grover, and Annabeth arrive. The dog is scary and is about to attack them, but Annabeth distracts him with a red rubber ball. In the movie, Percy comes across three hellhounds when he is in the underworld, but he does not specifically confront or see Cerberus.