So what are the Eternum exactly?

Rek'Sai and Nocturne have them, ones a void creature and the other is.. well from the shadow isles but basically a physical representation of the realms' nightmares

and they're both basically galvanized with futuristic metals (t-1000) from a different plane of existence and they receive a chilling echoing voice over and have a reddish glow around their eyes and certain conjoined points on their bodies.

Are they robots? Or enhanced beings. Or.. idk