While I can't tell you what kind of personality that might be, I definitely have met people like that before, and it's difficult when you're the one who is being lied to. Recently I went through an experience where I knew the person was a liar, but was in a way held captive by what they said to me, and chose to believe that maybe they weren't lying. If someone is an expert liar, it really does have that kind of effect on you.

I don't know if this is a certain personality as much as a learned behavior, or maybe a defense mechanism. People may lie to protect themselves, or in some cases for personal gain. There are many different types of people like this, and they lie for different reasons. But I think the important thing here is first learning to weed them out and protect yourself from them, before you trust them.