The Creation

Qor made everything in one form of existence, Aeviternity, that which began but can never end. In Aeviternity, he created other beings capable of creation calling them Aeviternals. To these Aeviternals he each gave a realm to form in their own image. These realms and Qor all existed in harmony in a place called Eternity.
Usos, an Aeveterinal of Qor, was frustrated that he had a beginning; that there was a point in the past that he could not reach. Despite his reach of an infinite future, he sought the same supremacy over other beings that Qor possessed over him. First, he experimented with temporality, creating the first Archaeviternals: beings that could exist in the infinite moments of their past, but were locked into a single moment that slowly marched forward with time. In this realm where time marched forward he called Aeviternity and made himself its lord. This satiated Usos for a time, but it worried the other Aeviternals. They saw his lesser creations as a denigration of existence, a casting down of the holy order established by Qor.
This sparked a war between the Aeviternals and Usos as they fought over the existence of Archaeviternals. The Archaeviternals split into two groups: Archfiends who supported Usos and Archcelestials who rebelled against his rule. Qor sought to quell the fighting, but could not destroy his own creation, which would violate the laws he wrote that held together existence. Instead, he would cast Usos into a realm of infinite endings, forever shrinking and being destroyed, yet never fully ceasing.
Usos learned of this plot and instead exploded the walls of time and space once again creating a new realm in which to hide from the influence of Qor. This split the planes once again, making the Temporal Planes. In doing so, he debased himself into a new form of temporality: an Immortal, the first being to experience time in a single moment and the beginning of the planes of existence outside of Celestia. Qor could no longer reach Usos, his influence thwarted by his own inviolable laws. His loyal Aeviternals, along with legions of Archcelestials would not leave heaven to chase Usos and risk their divinity.
Usos fled with his Archfiends and created the foulest form of existence, that of a mortal. Over these mortals, he ruled with chaotic disregard, blessing and cursing those who he chose. He created other immortals, Demons, and Devils, to enact his will across the many worlds of his unparalleled kingdom. In this time, every mortal had a beginning and an end, and after their destruction there was nothing.
Qor, having always sensed this reality, but requiring the events to occur according to his will, changed his inaction towards Usos to righteous hatred. He decided to save the mortal from the anihillation, the antithesis of creation. He appointed Aeviternals who were with him in Eternity to descend into the Temporal Planes and hunt down Usos and his minions. This began the War of Endings and spread throughout the many Temporal Planes. Every Aeviternal was tasked with rescuing people from the planes and worlds of Usos. For each mortal people rescued, Qor would bless them with a speck of eternity in their hearts, Quintessence, the very first soul. Should these mortals assist in the war against the minions of Usos, the Aeviternal they worshipped would vouch on their behalf to Qor, and they would be granted immortality and a place in Aeviternity. Conversely, those who believed Usos' lies and assisted The Forsaken Fleshweaver would instead be cast down with him.
The War of Endings spread throughout the temporal planes, many of which were destroyed in the process. Usos' armies began to shrink, his power of creation slowly dwindled and his immortal form was no match for the celestial hosts. Sensing a slow and brutal end, Usos gave himself up, returning to Aeviternity to face judgment. There, equipped with the full power of Qor, the Aeviternals created the Ending of Endings, a special realm of hell designed to crush the infinitude of Usos yet never fully destroy that which Qor deemed aeviternal. With their leader destroyed, the minions of Usos fled into the corners of the temporal planes.
Though hiding, the devils and demons still wrought havoc upon the many worlds they visited. Instead of the open chaos and destruction, the forces of evil worked from veiled fortresses and hidden alcoves. A few Archfiends still wielded power enough to challenge the Aeviternals and threatened to stretch the war back into Aeviternity. Many Archcelestiasl were slain in elaborate plots during this time. However, mortals began to flourish during this time. As their populations grew, they provided a convenient shield for the force of evil and a constant source of allies for the forces of good. This time was known as the War of Veils. Shadows became the battlefield, and secrets were the weapons of choice. The very fabric of reality seemed to fray under the weight of countless hidden schemes, as the conflict shifted from the heavens to the hearts of mortals. Unseen, the war raged on, shaping the destinies of entire worlds without their knowledge.
On Halor, The Divine Quinternion watches over the world. Some believe the War of Veils continues and every perpetration of evil is a secret extension of some unseen fiend. They believe the Quinternion stands as a vigilant guard against chaos. Others have moved on, seeing the world as a long-forgotten battlefield, the last war that scathed it lost to the Age of Demons and the lingering deities a transactional entity for a life after mortal death. For this latter crowd, these wars of the past are of little concern; the future lies in the hands of the puny mortals, now left to their own devices for the first time in history.