X-COM

XCOM is a series of sci-fi video games surrounding an Extraterrestrial Combat Unit setup by the nations of Earth to combat an alien invasion.

The series includes:

X-COM: UFO Defense (1994), X-COM: Terror from the Deep (1995), X-COM: Apocalypse (1997), X-COM: Interceptor (1998), X-COM: First Alien Invasion (1999), X-COM: Enforcer (2001), X-COM: Genesis (cancelled), X-COM: Alliance (cancelled), XCOM: Enemy Unknown (2012), The Bureau: XCOM Declassified (2013), XCOM: Enemy Within (expansion of XCOM: Enemy Unknown - 2013), X-COM 2 (2016).