I play board games with some friends. While we're generally nice guys and girls, in some of the games we go full twirling moustache evil, every trick allowed as long as its in the rules. That's an in-game persona for an hour, after which we revert back to our nice selves. Which is fine, BTW, we're consenting adults and we know its a game.

I always thought of Bill as doing the same thing in Microsoft. Nice guy generally, but business is business, no hard feelings while he steamrolls your small company to death. Then, after having a fun work day doing what he should be doing, he reverts to his nice self.

He was probably shocked to learn the world knew only his evil side.