Protagonist of this game is pretending his/her personality.

For example, the protagonist may be seeming to be a well-mannered man (always polite and calm, offering help), but this is just a facade which hides his true personality - one much more forceful and prone to be rude.

Note that this doesn't necessarily make the protagonist evil or a traitor. Do not use this tag for disguising characters like spies, assassins etc.