Chiron's wheelchair in the Graphic Novel.
Chiron's Wheelchair is the magical wheelchair which Chiron, a centaur, uses to disguise himself as a physically impaired human. Percy Jackson always wonders how he could get his backside into the wheelchair. He has come to the conclusion that the wheelchair was magical like the Hunters' backpacks, which are enchanted to hold numerous items.
Percy Jackson and the Olympians
The Lightning Thief
Chiron uses his wheelchair to hide his horse body so he could be Percy's Latin teacher, using the name "Mr. Brunner" while at Yancy Academy. He stays in the wheelchair for most of his tenure at the school, only exiting the chair when he is alone with Grover Underwood. He is also seen using his chair at Camp Half-Blood while playing pinochle with Mr. D. He eventually leaves the wheelchair to show Percy his true form and show him around the camp.
The Titan's Curse
Chiron was in his wheelchair when he first met Nico di Angelo.
The Battle of the Labyrinth
Chiron was confined to his chair because he was injured during the Battle of the Labyrinth.
The Last Olympian
Chiron is in his wheelchair form when he exits the van at the bottom of the Empire State Building when Percy calls them, so as not to alarm mortals.
Film
The Lightning Thief
Chiron's wheelchair in the Percy Jackson and the Olympians: The Lightning Thief movie.
In the film, Chiron is seen in his wheelchair during the first part of the movie, up until Grover Underwood and Percy leave the museum. The next time they see him, he is in full centaur form. The wheelchair is never seen without Chiron in it in the film, although before the Capture the Flag game, Luke said to him, "Chiron, you still got your wheelchair? Kid's gonna need it," referring to Percy who did not yet have a helmet, although he was only joking.