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)