What word best describes a person who is deceitful and very complicated to understand? As they say, he wears several masks.
Some words related to deceitful are duplicitous ("Given to or marked by deliberate deceptiveness in behavior or speech"), double dealing ("Cheating, dishonest; treacherous"), and aforementioned two-faced ("deceitful, hypocritical or duplicitous"). Analogous to previously-mentioned multifaceted is many-sided, meaning "Having many aspects".
Wearing several masks and being very complicated to understand are two very different things.
For someone who wears several masks, there are other answers on this page which I quite like.