Kryptonian

Kryptonians, natives of planet Krypton, were the fulcrum of events that altered the entirety of the cosmos some 50,000 years ago.

Kryptonians were engineered by Celestials as part of a long-term analysis of survivability in low-light environments. Their weak red sun forced significant evolutionary adaptation in a short timeframe.

While dwelling on Krypton, most Kryptonians seemed no different than any other mammalian race. It was when they discovered space travel-- in primitive, lurching rockets-- that their true potential was discovered. Standing under the light of a strong sun, the equivalent of mitochondria in their cells were triggered into overdrive. They absorbed latent energy all around them, including drawing upon the endless power of Hyperspace.

Empowered thus, the original Kryptonians were creatures of incalculable strength. Even those of average ability could lift dozens of tons and endure tremendous variations in temperature and radiation exposure. Senses were enhanced to the point of being able to sense objects even through barriers, and hear discrete noises from vast distances.

More problematically, they had no easily exploited weaknesses. It could take days to de-power a Kryptonian in a blind cell-- no easy feat. In the end, containing the Kryptonian threat required a complex and multilayered solution from Oa, Guardians of the Universe. Using magical might from the Demiurge, armies from Asgard, a complex strategy of biowarfare, andtheir newly formed Green Lantern Corps, the Oans finally beat the Kryptonians back to their home planet and irradiated the upper atmosphere with the only absolutely lethal substance known: Kryptonite.