Warning: This page contains major BioShock spoilers. Proceed at your own game-ruining risk!
Atlas is your enemy
His is the first friendly voice you hear in Rapture. He's your guide, he's your trusted source for information and he's the only thing that seems sane and normal in this frighteningly demented world.
He's also a total fraud. Early in the game, you'll hear about a crime and business czar named Frank Fontaine who gathered a worker's army and fought for control of Rapture with its founder, Andrew Ryan.
Well, Atlas is Frank Fontaine. He faked his own death, invented a new persona and transformed himself into the common man's hero. His aim - total domination - was always the same, but he found that he could accomplish more through false charity than through direct force.
To see the shocking transformation from friend to enemy, hit Play.