Premiering in 1993, this series of computer games were published by Mythos Games and MicroProse. The first 3 games are tactical games but the fourth plays as an action-based strategy game.
The general premise behind the franchise is that the player is in charge of the X-COM, the Extraterrestrial Combat Unit, and must defend the Earth from the invading alien forces.
In 2012, the series was rebooted with the release of XCOM: Enemy Unknown. A second game in the rebooted series, The Bureau: XCOM Declassified, was released in 2013.