Basically, it’s just doofus jerry lore. Matt, Edd, and Tom didn’t exist in his world. He succeeded with his robot, which made it easier for him to conquer the world. But all that success, he still felt like something was missing like it still not good enough--
So, he invented a way to travel between dimensions and eventually discovered Edds world.
His scars and missing arm came from an explosion during the war (This only caused him minimal damage compared to what Tom did to him in the og)