Before the currently known races of the Zulu Sector achieved space flight, or even achieved sentience, there was a race of highly advanced beings known as A'rthans. Their influence spanned the entire galaxy, and their technology had advanced to the point where their abilities seemed almost divine. Many of the current races were influenced by the work of the A'rthans, and some, like the Akyrians, HKorjorans and Shyedarians, were the direct result of A'rthan experiments.
In the current age, the A'rthans themselves have vanished. There are occasionally rumors that some still exist, but their influence has all but left the galaxy. However, their legacy remains in the technologies they have left behind: A'rthan artifacts are prized resources, because all of them have capabilities not possible with current technology. Examples of A'rthan artifacts that are in use or have recently been used are the Dysonsphere, Black Goo, the Planetsmasher, the Spatial Portal Device, and the Shyedarian Change Virus.
The most infamous creation of the A'rthans is the dimensional being known as the 6-Y. The exact reasons the A'rthans created the 6-Y are unknown, but what is known is that the 6-Y grew beyond their control, and posed a threat to the entire galaxy. The A'rthans were able to trap the 6-Y in a pocket universe, but in the process they were trapped in a different pocket universe, and are now beyond reach with current technology. However, the 6-Y continued to grow, and now has completely filled the universe in which it exists. Having no more room to grow, it now tries to burrow its way back into the universe of its origin, and occasionally breaks through with its tendrils to attack the beings living there. It has been fought back each time it has broken through so far, but it is feared that it may eventually become too strong to manage.