M-O (Microbe Obliterator) is a robot that is designed to obliterate foreign contaminants from the Axiom.[]
M-O cleans the Axiom
He chases WALL-E's dirt trail, as an attempt to clean the Axiom.
It is possible M-O is based on Mo from the Three Stooges, due to his debut scene with the other two robots that still remain nameless.