Virtual reality
Around the same time, Douglas Engelbart used computer screens both as input and output devices. In 1968, Ivan Sutherland, with the help of many students including Bob Sproull, created what was widely considered to be the first head-mounted display (HMD) system for use in immersive simulation applications. It was primitive both in terms of user interface and realism, and the HMD to be worn by the user was so heavy that it had to be suspended from the ceiling. The graphics comprising the virtual environment were simple wire-frame model rooms. The formidable appearance of the device inspired its name, The Sword of Damocles.
Ivan Sutherland
From 1965 to 1968, Sutherland was an Associate Professor of Electrical Engineering at Harvard University. Work with student Danny Cohen in 1967 led to the development of the Cohen–Sutherland computer graphics line clipping algorithm. In 1968, with his students Bob Sproull, Quintin Foster, Danny Cohen, and others he created the first head-mounted display that rendered images for the viewer's changing pose, as sensed by The Sword of Damocles, thus making the first virtual reality system. A prior system, Sensorama, used a head-mounted display to play back static video and other sensory stimuli. The optical see-through head-mounted display used in Sutherland's VR system was a stock item used by U.S. military helicopter pilots to view video from cameras mounted on the helicopter's belly.