The Rainers are a species of bipedal humanoids that inhabit the galaxy.
The Rainers are a species common to the wider galaxy, and are members, or at least play a more citizen-based role, of the Nova Empire, as a family of Rainers was present on Xandar during Ronan the Accuser's attack.
Ego planted one of his seeds on the Rainers's homeplanet in order to absorb it in his galactic Expansion, using the combined powers of his son Peter Quill and his own. The expansion of Ego's bio-mass caused havoc and the deaths of many Rainers, but it was eventually stopped when Ego was killed by the Guardians of the Galaxy.
Rainers are bipedal beings with a human-like body structure, but physical similarities between them and humans end there. The Rainers have brown wrinkly skin, pointy ears, four fingers, and cybernetic scalp implants in the place of hair.