He is an angry old junkyard owner who is rumored to own a ferocious dog named Chopper that he has trained to attack specific body parts. Chopper does exist, but he is just a harmless golden retriever.
When the four main characters taunt Chopper after trespassing on Milo's property, he threatens to beat the boys up as he heard them tease the animal. He identifies one of the boys as Teddy, then slanders Mr. DuChamp who Milo calls "a loony up in the nuthouse in Togus", knowing he nearly burnt off Teddy's ear using a stove, which enrages Teddy, who would then threaten to kill Milo. After this scene, Milo does not make any more appearances in the story. The boys leave, and Mr. Pressman warns them to stay away from his junkyard, or else all the boys' fathers would be informed of what they did..."except the loony". Teddy nearly runs back to attack Milo, but is restrained by the other boys, who tell him to continue the search for Ray Brower.