A huge mutated person sealed permanently inside of an irregular diving suit. A pain in the ass to kill, and really easy to get killed by. Seriously! The first time you fight one you have a shotgun that's supposed to do f***loads of damage, and it doesn't work, and at the same time, he has a 30 inch diameter drill that's busy working it's way through your skull while you're shooting! But still very awesome. They moan like whales.
"The frigging Big Daddy keeps killing me. At least I'll respawn and get to have my ass handed to me again."