Warrhammer 40k: The Enslaver and the Warp Realm
Not all Warhammer 40k factions were made equal and free. Some were born monsters that lived for the destruction of others. Others were mere parasites, living on the very being of other races. One such faction was the enslavers and their host was known as the Psykers.
The Psykers were a group of young races created by the Old Ones to fight their wars. When Neocrons, led by Ctan overthrew the mode operandi of the heavens, the Old Ones fought back by creating worlds of factions that would seek out and eliminate the Neocrons.
However, in the midst of all their sufferings, the Psykers came under attack by the parasitic Enslavers. These creatures who lived within the Warp quickly found a way to be transported into other realms. They would use their psychic powers to overpower the minds of their hosts and then occupy their bodies and reign from within.
One by one the Psykers were controlled and overpowered by the Enslavers. The result was a surmounted victory for CTan and his Necrons. The Old Ones, who had no one to fight their battles, lost and slowly faded into yesterday.
In addition, the impact of these creatures and their wars reached the entire galaxy. The Psyker swarms eroded life wherever they went. While Ctan fled before then, moving from one galaxy to another. The creatures were unstoppable until the Psyker swarm, unable to sustain itself died off.
This created a barren universe that remained even until the time of the Old World. Nonetheless, as the creatures died with their host, the galaxy renewed itself and life returned to their worlds. These creatures had disappeared by the time the Human Empire was born.
Thus, mankind knows nothing of them or their origins. To complicate matters, there is not much documentation that sheds light on them. Some references, other names such as Krell, Psyrens, Dominators, and Puppeteers.
