The group known as the Grey Eight, or more properly the Thir'ral (thir meaning "eight", 'ral meaning "grey") in Valerian, were a small collection of Mages who spent most of their time and energy on magical research many hundreds of thousands of years ago.
The group was lead by Garin Varel, whom many consider to be the "Father of Magic." Varel was one of the original Valeri to discover how to access the Essence and manipulate magic. The other seven members of the group were his best students: Gaesric Shinara (perhaps the greatest mage of all time), Bariath Tormelin, Minaea Ilkeen, Mirasta Tarkaan, Pelinor Kyndra (who created the Great Cataclysm), Tarmin Danar, and Sirella Doral (also known as the "Witch of the Shrunken Isles").
This group made the vast majority of magical discoveries, and experimented with and recorded most of the original spells. Each of the students was required to maintain a copy of Garin's spellbook, with their own notes added to it. They used a Longevity spell, known only to the Grey Eight, to stay alive for thousands of years.
The Grey Eight were hunted by the Wizard Princes during The Cleansing, but only Garin was captured. He sacrificed himself so his students could escape. The students went into hiding, and none of the remaining seven were ever found by the joKara.
It is unknown how many of the Grey Eight remain alive today. It was discovered (after the fact) that Sirella was still alive, at least until she met Brenn. And Bariath was the mage who founded Velloria and the Mage's Academy.