Game: BioShock
What Makes Him Bad: Pretending to be your ally in order to orchestrate a complicated plan? Not cool.
What Makes Him Cool: Were you ever going to figure out what "Atlas'" deal was? We didn't think so.

The friendly Atlas who appears to be guiding you through the depths of the strange new world you find yourself in is actually Frank Fontaine, who once clashed bitterly with his rival (and creator of the game's setting, the underwater dystopia Rapture) Andrew Ryan. Not only was Fontaine instrumental in bringing about the downfall of Rapture, but he's content to use you as a puppet as well.