The Celestials, towering creatures of tremendous energy, are survivors of the collapse of the First Firmament. They are among the oldest of races, billions of years old. They appear as massive bipedal beings hundreds of meters tall, wearing what appears to be armor of distinctive and unique design.
After the collapse of the First Firmament, they began experimenting with creating other races to try and harvest their genetic code and potentially find a means for creating new Celestials, to grow a vessel that could contain a Celestial’s endless power. They swiftly ran counter to the Oans, a race of brilliant, zealous supporters of law and order. Their war, cold and hot alike, would rage for billions of years.
To counter Oan military expansionism, the Celestials engineered many species. Descendents of their genetic programs led to the Kryptonians, Skrulls, and Eternals-- and eventually, to influence the wildcard genes of Homo Sapiens, creating mutants, Homo Magi, Homo Immortalis, and other unique bursts and leaps of evolution. Celestial DNA could interact unpredictably with various species, resulting in races with peculiar evolutionary adaptations and incredible abilities.
Immortal, unstoppable, the Celestials spread their genetic information across the universe in their search for a perfect species. And at times they would eradicate their own creations to harvest their genetic data for their mysterious ambitions.