Eysveig was a disembodied thinker. He was created in the Creation War by the Nine-Tongued Worm. Like other disembodied thinkers, he was made to help manage the vast numbers of troops under his master and to coordinate their activities in a conflict spanning systems and worlds.
Eysveig brain was composed of hundreds of brains merged together in some hideous dark experiment. These brains came from captured celestials defending Sphere 380. Eysveig is a lesser version of the disembodied thinker Ingu'lumin. He was made to be less smart than his predecessor because the Nine-Tongued Worm did not want another minion more smarter than himself.
Typically, one brain showed dominance over the others, slowly consuming the others, and adding their brain power to its own. The disembodied thinker was then exposed to some force, perhaps psionic, which lobotomized the brain to a point where it was subservient to a primordial master.
In the Creation War, Eysveig saw action on the continent Šadullu. While marshaling an army of storm archons for an attack on Tiwa'erra, his spies captured Silvanus's agent Buldapulax. In Eysveig's Infirmary, this hapless victim would end up becoming a primordial like his captors. Eysveig and his army of storm archons were wiped out when Ptah self-destructed the floating battle station Tiwa'erra.