He is a robot aboard the Axiom, programmed to clean items deemed "contaminated". M-O is obsessed with keeping things exempt of "Foreign Contaminants" and he can and will do anything to complete those tasks (an example is when WALL•E teasingly wipes the dirt off one of his treads and covers M-O's face with it, he screams and franctically tries to clean his own face). He travels around on a single roller, equipped with cleaning tools. M-O eventually befriends WALL•E after all his attempts to clean the dirty robot, following him all over the ship. His timely arrival in the garbage disposal area proves significant when he unintentionally wedges himself between the closing doors to prevent WALL•E and EVE from being jettisoned out into space. He then fully cleans WALL•E and accompanies him and EVE into bringing the plant to the holodetector on the lido deck so the Axiom can jump to Earth. However, WALL•E accidentally drops the plant when he sideswipes the holo-detector and the plant is thought to be lost until M-O finds it with the help of his functionality that detects foreign contaminants and has other robots and humans pass it all the way up to EVE. After they arrive back on Earth, M-O ushers the other robots into giving WALL•E and EVE some privacy as they share a tender moment.
Basic Parts: A brush instead of arms, a white body, yellow eyes on an LED screen, a siren, a blue brush cover, a roller, a backpack, and extendable black parts.
M-O is a neat-freak. He is obsessed with keeping things clean and tidy. His obsession with cleanliness is so great that he followed WALL-E all around the Axiom (he used WALL-E's dirt trail as a guide).
In the movie, there is only one M-O unit shown, but in the video game, there are two.