Their origins were described in detail in "Avengers Annual" #20. Following the Great Cataclysm (18,000 BC), the Deviants retreated to Subterranea. But their human slaves were unable to adapt to their new environment. Leaving the Deviants without the slave work force they needed. So they started genetic engineering experiments on the human slaves. The result was the birth of the Gor-Tokians Subterraneans.
Initially there were only two samples of this race: Gor-Tok and his mate Thera. But the experiments were deemed successful. They were physically stronger than their human ancestors. They were able "of seeing in virtual darkness". Making them far more suitable of living underground than most of other humanoid races of Earth. So the Deviants set about creating more of them.
The Gor-Tokians were subjected to "brutally hard labor". Responsible for building the new underground cities of the Deviant civilization. Gor-Tok eventually led his own slave rebelion. They won their freedom through a war. Gor-Tok became their first king and the namesake founder of their race. They soon gained a subspecies of their own. A number of Gor-Tokians started worshipping the demon Cha'sa'dra. Their new master transformed them to the first Lava Men.
The Deviants did not rest though. They needed new Subterranean slaves. They returned to the genetic experiments and created a new breed of Subterraneans, ancestors of the Moloids and Tyrannoids. These were docile and weaker than the Gor-Tokians. But produced in far greater numbers. The Deviants decided to use their new slaves as an army against the Gor-Tokians. Hoping that they would be able to reconquer the latter. Counting on numerical superiority.
The Deviants were sadly mistaken. The outnumbered Gor-Tokians were far more warlike than their opponents. The Deviants' armies were massacred. The Deviants found themselves fleeing from their own creations. Hiding in a hand-full of cities which were at a safe distance from the advancing warriors. The Subterranean (Moloids) were left directionless.
Over the following millennia, the Gor-Tokians fought "innumerable wars" against other species leaving in the Underground of planet Earth. The Underground rarely knew peace. They forged their own Empire and build many cities to house their expanding population. In the mid-20th century, King Krono prepared the Gor-tokian Empire for their next step on their evolution. They would invade the surface world to seek new challenges and obtain slaves for themselves. He prepared his son Gor-Tok II (Grotesk) to become the primary leader of their invasion force.
Their dreams came to an end when humanity started their underground nuclear testings. (Historically the first such test took place on November 29, 1951). The capital city of the Gor-Tokians was destroyed by a nuclear explosion, taking with it Krono and most of its population. Gor-tok II survived and became the new leader of their culture. But their entire species was dying. Those not killed by nuclear blasts and the tremors that came with them, were killed by radiation poisoning.
By the end of the process, only Gor-tok II and his consort Ingar were still alive. Ingar was the last to succumb to the poisoning. She died in the arms of her mate. Leaving Gor-Tok the sole survivor of a civilization which had lasted 20,000 years. He wasn't destined to die. The radiation which killed his race mutated him. Giving him Hulk-like strength and enhanced intellect. Though his mental condition was unstable.
Gor-Tok II would become Grotesk, a persistant foe to the x-Men and other heroes.