An impressionist or a mimic is a performer whose act consists of imitating sounds, voices and mannerisms of celebrities and cartoon characters. The word usually refers to a professional comedian/entertainer who specializes in such performances and has developed a wide repertoire of impressions, including adding to them, often to keep pace with current events. Impressionist performances are a classic casino entertainment genre.

Someone who imitates one particular person without claiming a wide range, such as a lookalike, is instead called an impersonator. In very broad contexts, "impersonator" may be substituted for "impressionist" where the distinction between the two is less important than avoiding confusion with the use of "impressionist" in painting and music.

Usually the most "impressive" aspect of the performance is the vocal fidelity to the target – usually a politician or a famous person. Props may also be employed, such as glasses or hats, but these are now considered somewhat old-fashioned and cumbersome: the voice is expected to carry the act.

Because animated cartoons often lampoon famous people (sometimes obliquely), a facility for impressions is one of the marks of a successful voice actor. Many cartoon characters are intended to be recognized by the audience as evoking a specific celebrity, even when not explicitly named. With such indirect references, the entertainment value does not lie so much in the technical achievement of exactly reproducing the voice so much as in merely making it recognizable; the joke lies in the reference to a celebrity, not in its rendition.