The Inhumans are ancient descendants of a tribe of nomadic Siberians who dwelt on the Earth some 50,000 years ago. Inhumans are universally metagenetic, due to ancestral exposure to Terrigen Mists.
The first Inhumans were created by an exiled member of their tribe. Vandal Savage had been exiled from the large tribal camp for his murderous barbarism, beyond the tolerance of even a society accustomed to hard choices in a cruel winter land.
Dying of exposure, Savage sheltered in an abandoned Kree science vessel. He was able to learn some of their language and even operate the ship's controls. Discovering that the Kree had been experimenting on human subjects, Savage used the ship's automated defenses to kidnap many members of his former tribe and subject them to the same tortures. In particular he exposed many of them to the Terrigen Mists, believing it to be a torture device.
Instead, dozens of tribesmen developed godlike powers, diverse and unpredictable. They broke free of their restraints and overtook the ship. Savage was left for dead. Now the sole occupants of the colony vessel, the tribe learned to operate the ship and soon it relocated to warmer climes. This colony/science vessel was easily the size of a small modern city and would become their wandering home for many millennia.
Inhumans discovered they had vastly increased lifespans compared to other humans. And virtually every pairing of Inhuman produced a child with an active metagene. However, low birth rates and attrition required the Inhumans to periodically recruit humans into their ranks.
The Inhumans kept themselves otherwise isolated from the rest of the world as much as possible. They had sporadic interactions with Atlantis while that nation was at the height of its power, and periodically encountered alien visitors such as Eternals making a trip to Earth. The Colony ship would be moved several times over the millennia, largely in response to shifting global climate conditions or proximity to warfare.
In 1500 BCE, the rebel king of Wakanda launched the Wakanda Civil War. His armies attacked the Inhumans, creating the first major military engagement the Inhumans had experienced in millennia. The war resulted in largescale loss of life for both sides, and the colony ship was destroyed mid-retreat as an uncontrolled engine malfunction ripped the hull in half. The vessel was scattered over thousands of miles, the bulk of the ship (including power core) crashing in the frigid Arctic north.
The surviving Inhumans, searching for a new home, discovered the lost Atlantean city of Atillan just off the coast of Ireland. They were able to use Kree technology to repower the mystical engines that once kept that floating city aloft. With a part of Atlantis resurrected, the Inhumans once more sought privacy and relocated their home again, this time settling into the warm climes of the Mediterranean coast.
In 1913, rumblings of war prompted the Inhumans to relocate once more. This time they moved Atillan to the Himalayas, far from the conflicts of humanity. As war raged across Europe the Inhumans rallied their resources and lifted the ship entirely from Earth's atmosphere, to park on the dark side of the Moon. There the city remained, with the Inhumans out of reach for most of a century..