Mecha-Satan is the evil huge robot devil that rules the underworld and does deals with humans like V.G and Bobby McMuffin occasionally.
Originally he was not a robot, but a very powerful demon named Satan that ruled the Old Earth. (See page "The History of the Deedle Universe") Satan was mortally wounded when the Cat Gods threw another planet at it. The demons had to relocate to The Underworld, a non physical plain near the Earth. Satan was extremely injured, and they began to rebuild his body, turning him into a robot. Mecha Satan then made a shape shifting machine thingy, to turn him into a snake to sneak into Earth. Earth was now populated by humans, and was a sort of paradise. Satan-Snake sneaked into the Earth, and planted the Hellspawn Tree, a project they had been working on. The Hellspawn tree instantly created Evil and corruption on Earth.
Mecha-Satan lives in a palace in the Underworld, ruling all of the demons of Hell. He also does many deals with humans, like the deal with Bobby McMufffin to make him powerful, (See page "Bobby McMuffin") the deal with V.G to make him immortal, and the deal to make him mortal again, (See page "The four corners of V.G") and the deal with Donald McRonald. (See page "Donald McRonald")