Imposture (noun)

1. The act of pretending to be someone else; the act of assuming a false identity.
2. The act of deceiving or fraudulently claiming to be someone or something else; a fraudulent deception.

Origin:

Early 17th century: from french, from latin impostura, from imponere "to impose upon".

Examples:

1. The imposture was discovered when the real person came forward.
2. The imposture was exposed when the fake credentials were checked.
3. His imposture as a doctor was soon revealed when he couldn't answer basic medical questions.
4. The imposture was motivated by a desire for financial gain.
5. His imposture as a war hero was exposed by the media.