The Qax are an alien species created from chaotic forces (first in liquid before evolving to form parts of gas giants, brown dwarfs and eventually the quantum fabric of the universe). They are few in number and as such not naturally warlike, instead they focus on trade.
The Qax had a longstanding alliance with the sentient Spline ships who carried them around the galaxy. Circa 5088 AD the Qax encountered humanity and a brief war was fought leading to the occupation of Earth and the colonies by the Qax. The Qax rule was brutal and they withdrew the anti-aging AS treatments removing the virtual immortality that humans had gained over the past two thousand years.
Circa 200 years after the invasion the GUT ship Cauchy appeared in the Sol system towing one end of a wormhole created 1500 years before. The audacious plan of humanity from that time period had been to contact their own descendants using it, however the Qax rapidly took over the ship but not before a human resistance group ("The friends of Wigner") escaped to the past. There they set about seeding Jupiter with black holes for their own purposes. The Qax invaded the past but the Spline involved were wrecked and the wormhole closed.
After this the Qax saw humanity as far more of a threat and took measures. All human cities were leveled and replaced with faceless grey structures while Earths biosystem was replaced with an artificial Qax based one and humanity was forced to speak a constructed language, all human history was to be erased.
Before this work could be finished the Qax sent a human, Jim Bolder, in a captured Xeelee nightfighter to investigate the Great Attractor where he found the Ring. Through careful planning he returned to the Qax home system in the wrong place and the Qax fired on the ship (Bolder having jumped ship moments before). Among the weapons used was a Xeelee starbreaker that had been recovered from the ship and the beam touched the Qax sun.
This started the sun towards a nova and the Qax were forced to abandon the occupation to save their own lives. The Qax vanished for centuries finding new places to live. In the interim humanity became a vast empire and the Qax never recovered their former power.
Long years later after the Xelee defeat of mankind the Qax are known to have dealt with any colonies that were missed by the Xeelee. Unlike other races, the Qax waited to flee through the Ring after the Xeelee were defeated since their methods of support could sustain them even in a dying universe. They knew the Ring was doomed but they also believed they had time to finish their own projects first - foremost was finishing the job of annihilating humanity.
Around four million years AD the last humans emerged from their Xeelee prison and set out for the Ring, guided by another human Paul who had been transformed into a quantum based lifeform by the Xeelee.
Knowing that the Qax and the photino birds would try to destroy the humans' ship, Paul used his connection to the Xeelee to create an illusionary shadow fleet of Xeelee making the photino birds believe a re-invasion was in progress. The birds rushed to the Ring and began efforts to close it for good.
The Qax learned of this and put their might to stopping the birds and securing the Ring from destruction. A Spline fleet assaulted the birds (even using a star accelerated to light speed) but ultimately most of them were killed and they failed. During this battle the humans slipped through the Ring (though not Paul who due to his status was trapped in this reality) and the loss of the Ring trapped the Qax forever.
Millions of years later Paul tired of watching the plans of the photino birds evolve slowing over time, and placed his mind in orbit round a dead star that was being heated a few degrees above zero. After a period he found he was not alone - the last Qax (also now quantum based) had joined him. The two old foes orbited the star and exchanged no words. There was nothing left to say.