UFO: Enemy Unknown (marketed as X-COM: UFO Defense in North America) is a science fiction strategy video game developed by Mythos Games and MicroProse. It was published by MicroProse in 1994 for MS-DOS and Amiga computers and the Amiga CD32 console, and in 1995 for PlayStation. Its European PlayStation release is titled X-COM: Enemy Unknown.
The story of X-COM, set in the near-future at the time of the game’s release, begins in the year 1998. The initial plot centers on increased reports of UFO sightings as tales of abductions and rumors of attacks by mysterious aliens become widespread. The nations of the world come to perceive this as a threat and attempt to form their own forces – such as Japan’s Kiryu-Kai force – to deal with the crisis, but these efforts are unsuccessful. On December 11, 1998, representatives from some of the most powerful nations in the world secretly meet in Geneva to discuss the issue. From this meeting is born the clandestine defense and research organization Extraterrestrial Combat (X-COM), over which the player assumes control at the start of the game.
In the beginning, the player will only have access to conventional weapons, but as the game progresses, the player learns more about the enemy, their species, mutated creations, and technology. It is ultimately revealed that the “leaders” behind the alien invasion are a race known as Ethereals which possess powerful mind control abilities and enslave other races of aliens to perform their bidding and that their main base in the Solar System is located in Cydonia region of Mars. The player must then prepare the final assault team, attack Cydonia and destroy the mastermind behind the alien invasion, the biocomputer Alien Brain.
The game may end in several ways. If the player’s performance is poor or worse for two consecutive months, the player runs a deep deficit for two consecutive months, all the player’s bases are captured, or the player mounts an assault on the aliens’ Mars base and loses, the game ends in defeat in which the council of funding nations makes a futile attempt to negotiate with the aliens. If, however, the player is victorious in the final attack, the game ends in mankind’s victory.