The noun charlatan means someone who pretends to have a skill or knowledge but does not really have.
Synonyms are swindler, con artist, fraud, or imposter.
The word origins from French (16th century) charlatan meaning “mountebank, babbler”, from Italian ciarlatano meaning “a quack” (source also from ciarlare meaning “to prate, babble”, and ciarla meaning “chat, prattle”, perhaps imitative of ducks’ quacking).
She could hardly believe that her partner was a charlatan.
He does not know anything about medicine – he’s a complete charlatan.
The most famous charlatan was exposed and arrested last night.