Goofy is related to dogs, perhaps in the same way humans are related to apes.
It seems that there’s no official word on what Goofy is, if not a dog, but Bill Farmer has his own theory, which I suppose makes sense.
Instead, Pluto is a dog, and Goofy is something else.
Before he was Goofy, the character was known as Dippy Dawg, and so, it was clear that Goofy was supposed to be a dog in the same way that Mickey was a mouse and Donald was a duck, and yet, it seems that’s not really the case.