"Prey is a first-person shooter video game developed by Human Head Studios and produced by 3D Realms. The Xbox 360 port was developed by Venom Games. The game was initially released in North America and Europe on 11 July 2006, and later was made available on Valve's Steam system on 6 November 2006. Prey uses a heavily modified version of id Tech 4 to use portals and variable gravity to create the environments the player explores. The game's story is focused on Cherokee Domasi Tawodi as he, his girlfriend, and grandfather are abducted aboard an alien spaceship known as The Sphere as it consumes material, both inanimate and living, from the Earth in order to sustain itself. Tommy's Cherokee past allows him to let his spirit roam freely at times, and gives Tommy an edge in his attempt to stop the Sphere.
Prey had been in development in one form or another since 1995, and has had several major revisions. While the general approach to gameplay, including the use of portals, remained in the game, the story and setting changed several times. The game received generally positive reviews and was a commercial success, selling more than one million copies and leading to the development of a sequel, with rights owned by the Radar Group. The rights were recently transferred to Bethesda Softworks and Id Software parent company Zenimax Media."
Source: Wikipedia, "Prey_(video_game)," available under the CC-BY-SA License.