Mickey is a mouse, Donald a duck, and what the hell is Goofy?

Mickey "Mouse," Donald "Duck," Goofy "What ? " and if Goofy is a dog. Why is Mickey mistreating another dog, Pluto, like a retard he being naked and in a leash. That doesn't bother Goofy at all? Maybe Goofy is a bull since he dated Clarabelle the Cow.