The best way you make a characters look like they're one thing but are really another is to build your characters with seemingly incompatible traits. The trick is to show the "public" traits but conceal the "private" traits until the reveal. By conceal I mean use misdirection so that the effects of the private traits are either misinterpreted or associated with someone other than that character. This often works when assigning traits from the different character trait levels (motivation, methodology, evaluation, purpose).
For example, let's say we have a character that is both oppose and proaction. He can publicly oppose things while privately (and unknown to the audience) act as a provocateur by setting things into motion proactively. Eventually the hidden trait is connected by others (and the audience) to its proper owner and that character's "true" (complete) nature is revealed.