Master Belch is the leader of the ghosts that attack Threed. He is a big pile of Fly Dung basically. He loves one item: The Jar of Fly Honey. This is one of the easiest ways to defeat him. He also takes complete control of the Mr. Saturns in Saturn Valley.
Master Belch only appears in Earthbound. He appears under the waterfall by Saturn Valley, inside a room with something dripping off of the ceiling. He makes a weird sound when you approach him, which makes people try and mimic him.
He has no job. He has a goal. But, he does get people to work for him. They create Jars of Fly Honey for him on a conveyor belt. If they do not work right, he will lock them up in a cave. This is where he puts many Mr. Saturns. He does have a few Zombies working with him to stop Ness and friends as well. He is helping Giygas destroy the world, even though Giygas is not in the world in the time you are currently in. This means that he probably came from the future.