A demonstrator may be: A person performing a demonstration, such as to explain science or technology A person demonstrating a product for sale live or in an infomercial An attendee at a political rally An academic rank A vehicle adapted to emergency service specification, and issued to locations for use as a prospective emergency vehicle if adopted to that workforce either police, ambulance or fire. A fountain pen with a transparent body originally used so dealers could show customers how they worked. See Demonstrator pen Demonstrator (film)