The Primes are a xenophobic, aggressively expansionist alien species originating in the Dyson Alpha system. They are a hive-mind species, comprising stationary "immotile" forms that command herds of "motile" forms. Immotiles have independent thought and cognition, whereas motiles are essentially mindless and are directed by commands relayed to them by their parent immotiles via direct neuron-to-neuron contact. In addition to breeding huge numbers of motiles, immotiles also give birth to other immotiles, who are initially slaved to their parent but given enough time or distance become independent. Their math is base 4 rather than base 10, a feature which likely originated in the prominent four-fold symmetry exhibited in the Prime bodyplan.
The race is extremely xenophobic, to the point that individual immotiles view the very existence of other independent life forms as a threat to their continued existence. Immotiles go to any length to destroy or control any independent entities, for example fitting their offspring with ever more advanced cybertech in order to forcibly keep them integrated and under control. This xenophobia is so extreme that the Prime exterminated all mobile life on their home world, lest it ever become a threat, and upon gaining nuclear technology immediately and unhesitatingly used it against each other, stopping only when the damage to their world became so extreme that it threatened the survival of the remaining immotiles. Upon contact with humans, the immotile collective known as MorningLightMountain immediately deployed wormhole technology to eliminate every other immotile, leaving it and its offspring (now always kept in range by wormholes so they remained a single extended consciousness) as the only representative of its race on the homeworld. It then proceeded to immediately turn all its forces against humanity, as the very possibility of not destroying them was beyond its comprehension.
At some point, the immotiles sent some of themselves to conquer the habitable planet orbiting the other star in their binary pair. The species that evolved there possessed advanced biotech, which these Primes applied to themselves, in the process becoming alien to the original primes, who dubbed them "alt-Primes". These Primes overwhelmed and enslaved the species living there, using their own biotech to turn them into a new kind of motile, before again turning on each other and the Primes on their homeworld.
At some point after this, but before the Prime could discover FTL, the Anomine discovered the binary system, and realizing how dangerous the Primes would be if they became fully spacefaring, appealed to the Raiel. The Raiel agreed with the assessment, and used a pair of Dark Fortress emitters to enclose both systems in 30AU forcefields, trapping the Prime and Alt-Prime in their respective systems. A single Alt-Prime managed to escape, purely by accident being outside the fields at the moment of enclosure, and made its way to Far Away, where it was able to send out a signal that eventually lured Humans to it. It then began a centuries-long plan to eliminate humanity by using intensive mind control to take over and undermine the commonwealth and manipulate them into going to the Prime homeworld (on a scientific mission to try and figure out what happened to the two stars), sending along an agent that sabotaged the Dark Fortress around the original prime world, releasing them in a war of mutual destruction. Known as the Starflyer, this plan almost resulted in the extermination of humanity before the Dark Fortress was resealed and the escaped Prime, including the StarFlyer, were exterminated.
At some point some Prime ended up inside the Void, but they were later ejected into interstellar space along with others who would not go along with the Void's purpose. A desperate attack by Laura Brandt and the people of Bienvenido destroyed them and their planet before they could invade, ending the last known Prime presence outside the still-enclosed binary stars.