Your standard super mutant is...a bit like if you crossed a gorilla with a brick wall. And then made it a cannibal. Oh, and painted it green.

They were humans once. They're a unique sort of monster in the wasteland in that they weren't twisted by radiation. They were experimented on, mutated intentionally to serve as super soldiers in a slave army. I'd feel sorry for them except that every time I come across a group of them they're more interested in fillet o' Deacon than brotherhood of man and sympathy. Even raiders are easier to reason with.