HoverBot - First Quadcopter Drone - Concept Demonstration in 1992

The HoverBot was invented by Dr. Johann Borenstein at the University of Michigan in 1992. It is believed to be the first ever drone based on a quadrotor or quadcopter concept. The project lasted for only three months before the funding agency, the Department of Energy, decided to discontinue the project because they felt it would be too dangerous to have drones performing video surveillance in nuclear power plants.
Within the 3-month lifespan of the project, the HoverBot did not accomplish free flight. Rather, the project ended with the proof-of-concept demonstration of the HoverBot shown in this video. The demonstration established that a quad-rotor drone was capable of stable hovering and that it was controllable in pitch, yaw, and roll, as well as elevation.
Keen-eyed viewers will be noticing the oscillating fan in the rear corner. This fan introduced turbulent disturbances to challenge the control system.
An excellent overview over the state-of-the-art in drone technology is provided in the Smithsonian Air and Space Magazine (January 2013) article: "Drones for Hire."