The Xians were an alien race from Planet X, a desolate world on the dark side of the planet Jupiter. They used a magnetic form of mind-control to send the giant monsters Godzilla, Ghidorah, and Rodan to conquer Earth. Their plan was eventually ruined by human scientists, who freed the monsters and destroyed the Xian spacefleet. Xians and their machines are highly vulnerable to certain frequencies of sound, which was their downfall.
In the Godzilla video game (for the Nintendo Entertainment System), Godzilla and Mothra battled against a new Xian invasion in the year 19XX, wherein the Xians utilized various destructive monsters including Ghidorah, Moguera, Mechagodzilla, Matango, and Gigan. A second invasion with both Showa and Heisei era monsters occurred in the Nintendo Gamecube's Godzilla: Destroy All Monsters Melee game.