In 1981, Scientists noticed the presence of a rogue planet approaching Earth. This planet was promptly called Gorath, and it was realised that Gorath would destroy Earth if the two planets collided, requiring a task-force to figure out how to deflect it.
After the Xiliens revealed themselves to the people of Earth and teleported away the monsters attacking the planet's major cities, their leader, the Controller of Planet X, explained that his race had come to save mankind from an impending disaster. He revealed that a gigantic runaway asteroid called Gorath was on a collision course with the Earth and would arrive and destroy it very soon, and that the Xiliens wanted to prevent this disaster from happening. However, Miyuki Otonashi and some of the Earth Defense Force's members concluded that Gorath was not real and that the Xiliens had more sinister intentions. Whether the Controller was being honest or not about this threat never came to pass, as he was usurped and murdered by X soon afterwards.
After the Xiliens' plan was exposed and the remaining members of the EDF boarded the Xilien Mothership, X released his trump card against Godzilla. X summoned the real Gorath asteroid to Tokyo, but Godzilla managed to destroy it with his atomic breath, creating a massive explosion that destroyed a large area of the city. However, Gorath was merely a vessel for transporting the Xiliens' ultimate weapon, the creature known as Monster X, who descended to the ground and challenged Godzilla.