My friend JimSmash sent me some Hulk comics! Sweet! Me like Hulk. One of them was this classic from 1977. Spoiler alert- the unexpected super-villain is none other than Bi-Beast! Yup, the clone robot thing with the dual nature (plus he has two faces on his head) that was made by some bird-people on a floating island somewhere. I was a little hesitant to google him but it turns out he isn't as obscure as I might have thought, and even cameoed on a relatively recent episode of Avengers:Earth's Mightiest Heroes. It says so  on his Wikipedia page.