"In the year 1994, from out of space comes a runaway planet, hurtling between the Earth and the Moon, unleashing Cosmic destruction."
The Great Cataclysm was such a catastrophic event that it destroyed a large percentage of Earth's population and demolished much of human civilization. The aftermath of this event led to several other races (such as Moks and Carocs) coming to control large sections of the planet.
There are several objects and a few people that were left over from before the Cataclysm.
The Wizard Mindok was apparently an ordinary human before the cataclysm.
There were several technological advances shown to have been made before the Cataclysm that do not exist in the real world. Examples include the Guardian machine that protected the Alamo and various mutated monsters that were said to have been created as a result of genetic research prior to the Cataclysm, such as the Sleeping Demon.