The Two-Facer

Bonus Points if they actually have more than one face.

The one who puts on a facade to trick others into believing they're a protagonist (a role like the Support or Helpist) when they're really an antagonist. The Two-Facer usually hides their true intentions until it's time for the truth to come out. It's common for the Two-Facer let the audience in on their secret with a Lone Evil Laugh or Menacing Grin to show that, no, they aren't a good guy.

Many roles can double as Two-Facers. One such role is the Twist Villain, a kind of Villain who fakes a good relationship with the Good Guys mainly for their own reasons from the moment they're introduced to the story. When it's time for them to cut the act (often around the climax), the Twist Villain could explain what their plan was and Break Reality to the Good Guys, saying that they aren't really friends with the protagonists and were only using them to get their way.