The Shock Villain

''That sucks how my Role Model turned out to be not as good of a guy as I made him out to be. Eh, it happens.''

The protagonist or neutragonist who turns out to be an antagonist by the end of the story. They uncommonly have meaningful ties with the Main Cast and often just lightly interact with at most a few members from time to time, but a Shock Villain could even be a family member with a dark secret they've been hiding for years up until The Truth Comes Out thanks to the Detective or Main (more often the Main than the Detective) uncovering it.