phony

A person who assumes an identity or quality other than their own.

“He claims to be a doctor, but he's nothing but a fast-talking phony.”

A person who professes beliefs or opinions that they do not hold.

“He's such a phony, he doesn't believe half of what he says.”

Anything fraudulent or fake.

Fraudulent; fake; having a misleading appearance.

“A good jeweler should be able to tell a real stone from a phony one.”