In 1993, X-Com: Ufo Defense was released. Known internationally as X-Com: Enemy Unknown, X-Com is strategy game game where the player assumes command of an international organization tasked with defending the earth from a methodical alien invasion. The game is widely considered one of the best computer games of all time, and numerous sequels and remakes have been created. IGN ranked X-com: #1 in the top 25 PC Games of all time, beating out Half-Life 2, Fallout, World Of Warcraft, and Call of Duty. IGN had this to say:

"It may be old as hell and you may have to actually disable DirectDraw to get it to run these days but there's still no PC game that can compete with the mighty X-COM. Conceptually it's one of the finest strategy games to ever appear on any system. Putting the player in charge of a worldwide defense against an alien invasion, the original X-COM combined elements of sophisticated base management, high-tech research, engaging roleplaying, thrilling tactical combat and a tense, terrifying story to create an experience that has yet to be duplicated by any other game. Leading your squads on missions to reclaim crashed UFOs or fighting house to house in an effort to repel alien terror attacks on major cities throughout the world were the highlights of the game but X-COM has plenty of other pleasures in store, from juggling personnel and equipment to keeping the nations of the world happy enough to sustain your budget. Simply put, there's no excuse for strategy fans not to break this one out and play through it again." - IGN

Additional Links:

X-Com on Wikipedia

The X-Com Wiki

XCommand (Fansite) (Fansite)