im·per·son·ate /im-'pər-sə-ˌnāt/ vt -at·ed, -at·ing: to assume (another's or a fictitious identity) without authority and with fraudulent intent
impersonate a police officer
impersonated a public servant by saying he was from the water department
im·per·son·a·tor /-ˌnā-tər/ n
Merriam-Webster’s Dictionary of Law. Merriam-Webster. 1996.