The Centaurians are a blue-skinned spacefaring race.
A Centaurian named Yondu Udonta was sold by his parents into slavery, where he served in gladiatorial battles for twenty years. However, Udonta was freed and recruited by Stakar Ogord into the Ravagers, where he and Stakar served together until Yondu was eventually promoted to a Captain, gaining his own crew as a leader as one of the 100 Ravager Clans.
After encountering the corpse marked as G.H. inside the facility known as The Guest House, Phil Coulson asked Lady Sif if she had met any blue alien species. When Sif replied, she listed, among others, Centaurians. She added that the Centaurians had never been on Earth, without knowing that one of the Centaurians, Udonta, came to Earth in 1988 to kidnap a young Peter Quill.
Centaurians are humanoid, with differentiating features such as blue skin.