to pretend to be someone else by copying their appearance, voice, and behaviour, especially in order to deceive people:
Do you know it is a very serious offence to impersonate a police officer?
to copy someone's voice and behaviour, especially in order to make people laugh:
In the film he amusingly impersonates a woman.
—impersonation noun [uncountable and countable]
He's renowned for his Elvis impersonation.