[Behemoth]

Maybe, but I've also heard a theory that GLaDOS just kidnapped Chell on Bring Your Daughter to work day, probably because of all the science experiments in the one part, hers was the most sciencey. I'm not sure though, I'm only halfway through the game despite reading a bunch of spoilers.

And oh, I haven't even touched co-op yet. Despite the taking over bit, is it fun?