Mutated gorillas. Can you imagine what a mutated silverback gorilla would be like? An already 900 pound musclebound beast of a creature, mutated by radiation, it'd be terrifying.
Or what if it somehow gets exposed to FEV and because humans and gorillas are somewhat closely related, the FEV works on it and makes a supermutant gorilla but unlike most humans, the FEV doesn't make gorillas dumber, it makes most of them smarter and you end up with this giant, bald, 2000 pound behemoth sized gorilla that can speak and is as smart as a normal human, maybe a little smarter. It's used its size and strength to take control of a group of supermutants and they all fear it just like a normal human fears a supermutant.