4. Atlas Bioshock
Bioshock would have been nigh on impossible to complete without the help of Atlas. He provides valuable information throughout the game whilst explaining the history of Rapture. It seems that on the surface Atlas merely wants Jacks help to rescue his wife and son, and for the first part of the game this is exactly whats happening. When Ryan releases the splicers into the submarine bay and Atlas loses his wife and child, no one would blame him for seeking revenge. He asks for Jacks help again and the game continues as you try to locate Ryan and end his reign. It appears that Atlas truly is your ally right up until you finally meet Andrew Ryan, who reveals that Atlas, who is also Frank Fontaine, has been controlling you the entire time through mental conditioning and the key-phrase Would you kindly.... What makes this betrayal all the more brutal isn't just the fact that you were used to kill your own father, but that Atlas was also the person behind the downfall of Rapture.