Kimera's exact physiology is unknown, they appear as humanoid energy beings possess ing chameleon-like abilities, allowing them to impersonate other creatures, aparrently to take on their memories and to genetically adapt in order to mate with them in order to produce Kimeran hybrids. It is not known though if they require two individuals for simple reproduction purposes.
The Kimera were said to be a race of interstellar researchers and spiritualists who traveled space and visited other species to bond with them using their unique genetic nature. When they came in contact with the Atavaus species some 8 to 10 millions ago, they altered and split that race into two new species with different Kimera traits, Jaridians and Tealons. They are believed to have been exterminated by the latter afterward and are now generally believed extinct .
Source: Earth Final Conflict