who are you really?

A friend said something to me that made me to think about who we are as humans. The thing is who are you? are you someone with different identities, or two faced or may be more faced. I observe that humans have different identities or personalities. can you explain how a man can be a different person in different locations. for instance a man is gentle in a church or a company and wild outside the church or company. what I'm trying to make you understand is people put on masks on their face so you don't get to know the real person behind the mask.