Inhumans are a subspecies of humans formed during ancient Earth.
At the beginning of the Kree-Skrull War, the alien Kree established a station on the planet Uranus, a strategic position between the Kree and Skrull empires. Through their work at this station, they discovered that sentient life on nearby Earth had genetic potential invested in it by the alien Celestials. Intrigued, the Kree began to experiment on Earth's then primitive Homo Sapiens, inspired from studying a dead Eternal.
Their test subjects, the Inhumans, went on to form a society of their own, which thrived in seclusion from the rest of humanity and developed advanced technology. Experiments with the mutagenic Terrigen Mist gave them various powers, but also caused lasting genetic damage and deformities. This led to a long-term selective breeding program to try to mitigate the effects of these mutations. Their city Attilan has frequently been relocated and, as of 2005 stories, rests in the oxygen-bearing Blue Area of the Moon.