Nouns

(n)imposter, impostor, pretender, fake, faker, fraud, sham, shammer, pseudo, pseud, role playera person who makes deceitful pretenses
(n)hypocrite, dissembler, dissimulator, phony, phoney, pretendera person who professes beliefs and opinions that he or she does not hold in order to conceal his or her real feelings or motives
(n)pretendera claimant to the throne or to the office of ruler (usually without just title)