What is a word to describe a person who 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".

The common English idiom nearest to your meaning is to speak of such a person as two-faced, though this strictly means someone is deceitful. To describe someone who is complex and hard to understand without implying deceitfulness, we might call them multifaceted.

Wearing several masks and being very complicated to understand are two very different things.

If you are after a word to describe someone who is very complicated to understand because they change often, then I like fickle or, perhaps a bit more metaphorically, volatile.

For someone who wears several masks, there are other answers on this page which I quite like.

You may say the person has multiple personalities, or is dissociated. If the person changes according to the ambience you could call him/her "chameleon".