At the beginning of time, the initial Precursors (known as the Elders) were created from a mysterious cosmic anomaly. While initially, the Precursors had no explanation for this anomaly, it was eventually concluded that this anomaly had applied only to them, and only within their universe. Amongst all other charted universes, no sign of a similar event was identified.
Among the Elders there were a total of 13. These initial 13 Precursors, through use of their abilities, were able to create and manipulate life and consciousness. In doing so, the Precursors would become responsible for all life seeded throughout the many universes that they would eventually navigate and explore. To start, the Elders created beings nearly identical to themselves. These beings would be no different aside from their capacity for powers / abilities that the Elders possessed. The creation of these beings would be the start of the ever growing Precursor species. For billions of years, the Precursors would grow their civilization, which called the Prima Infinitum Universe their home. Over this time, their species would entirely inhabit multiple galaxies throughout this universe, all through a singular central government, atop which the Elders ruled as Gods. The population of the Precursor race became inconceivable in size. The number of Precursors is estimated to possibly be as much as 10^60 throughout the entirety of their civilization. The Precursors possessed incredible technology that allowed the management and communication between the entirety of their species. Throughout the entirety of their history, nearly the entirety of their population stayed within the Prima Infinitum Universe. The exception to this would be the handful of researchers and explorers that would navigate and catalog the infinite universes within the overarching multiverse within which they existed. Among the Elder Precursors was Cassius, who was widely considered to be the strongest (in regard to physical ability and powers/abilities) of the entire species, including the other Elders. Cassius was renowned as an incredible and charismatic leader, as he was typically the spearhead of the species development. Many within the greater population saw him as their unofficial leader.
At a point within their history, Cassius would grow very close with another Elder, Giulia. The two of them became madly in love, eventually deciding to create a child together in their image. This was done by genetically mixing their own DNA to create an offspring (the elders do not have sexual organs, unlike their Lesser Precursor counterparts). This offspring was the first Lesser Precursor created by this method, rather than simply being conceived by the genetic material of a singular precursor donor. Their child would be known as Lilith. At some point later on, Lilith would begin to despise many of the rules and guidelines to which the Elders lived and governed the Lesser Precursors. She believed that the Elders were not Gods, and eventually renounced her parents and those who ruled. Over the next few thousand years, Lilith would form a resistance movement within Precursor society, and eventually incited a civil war. This war raged on for hundreds of thousands of years, as a large portion of the population began to believe that the Elders were deceptive in their ways. Eventually, after an assasination attempt on Lilith, supposedly ordered by her parents, Lilith fled from the war, as well as Precursor society as a whole. Using her powers, which were unique for a Lesser Precursor, Lilith opened an unstable hole in Slipspace to leave Prima Infinitum and begin her life anew in her own universe. By tearing this hole in Slipspace in such an unstable manner, she was cast beyond Slipspace, and any known universe, to something else entirely.
This new realm that she had traveled to was nothing but a dark wasteland, seemingly endless and lifeless. She traveled this wasteland for what appeared to her as an eternity, however in reality this realm was far beyond space and time. Eventually, she heard voices beckoning her. She would resist for a time, before giving in to the prospect of salvation from this hellscape. This would eventually bring her before something that she could not entirely comprehend, nor would a comprehensive description of this being really even be possible. What she encountered was an entity. Unknown to any of her senses, yet flooding all of them. She could not comprehend its shape, yet it occupied space, yet it seemed to not exist in any one space at any time. She could not understand the entity, but it spoke to her. It was not in any language that she knew, yet deeply, she understood. The entity spoke, and she listened. In what seemed like eternity, yet could be no time at all, the entity showed her a truth that could not be possible. A truth of life and death. Eternal torment. Hunger beyond that of what a stomach could experience. Whatever the entity was, she could not say. The entity swayed her to a confused mental state, by which it was able to control her actions. This state of mind was the beginning of what is known as corruption. Now with Lilith as its hand, the entity would use her to feed upon life within the multiverse that had now been revealed to the entity. Over the next hundreds of millions of years, Lilith would infest universes throughout the multiverse, indoctrinating all life that she could find. Over this time, much of it was unopposed as she moved through the multiverse. Eventually, the Precursors caught wind and tried to stop her. Every attempt to do so failed, as the influence of the corruption was too great, and her hordes of corrupted were too numerous.
Eventually Lilith and the corruption attacked Prima Infinitum. For millions of years the Precursors tried to fight back the horde of corruption, but were inevitably overwhelmed and forced to flee. Led by Cassius and the few remaining Elders, a few thousand Precursors escaped into Slipspace. From there, they jumped to a random universe designated BESE-MCXIII. This universe being the one that is home to the Milky Way Galaxy, where the surviving Precursors would establish themselves. In their time there, Cassius and the Elders dedicated themselves to creating a Slipspace inhibitor, capable of blocking all travel to and from alien universes, ultimately isolating BESE-MCXIII to itself.
This leads into the establishment of the Eternian Empire and the Eternian species.