Enslavers

"My psyker colleagues do not wish to speak of the Enslavers, but I must. The Ordo Xenos is aware of the horrible means that Enslavers use to gain a foothold in our realm, and I share their determination to prevent such an event from ever coming to pass. I do not wish to delve into details; all that is necessary to know is that these things present a peril beyond imagining, and must be crushed at all costs wherever sighted."
–From the journals of Inquisitor Felroth Gelt: 780.M41
Also known as Psyrens, Krell, Dominators, or Puppeteers, the
mysterious Enslavers are possibly one of the greatest threats for
not only the Imperium but all living beings. While they live at
least part of their lives in the Warp, they have material bodies
and can also exist naturally in the material realm. Their very
existence is a closely guarded secret, with only a select few
knowing what these beings truly represent, and the hideous
fate that could befall the Imperium should they overpower
mankind.
Descriptions of Enslavers are rare and fragmentary, but most
detail a grotesque, sickly pink–brown bulbous body. Tentacles
writhe underneath them, assisting in movement as they hover
through the air, while grasping mandibles are used to grip
their prey.
Inquisitorial Scholars are divided as to whether Enslavers
are sentient. While they seem to act in an intelligent manner,
they make no attempts to communicate or use tools of any
kind. Instead they use psychically controlled slaves to conduct
any physical work, and it is this power which gives them their
name. Enslaver victims become complete puppets to the alien’s
will, performing even the most self–destructive or heretical
acts without hesitation. While the Enslavers themselves can be
felled by regular weapons fire due to their corporeal forms, it
is their dominated thralls that often pose a greater threat, for
few can bear to kill their comrades even when clearly under
alien control.
Enslavers travel on the currents of the Immaterium and are
drawn to the psychic emanations of living creatures, especially
from unprotected psykers, who they can detect from many
light years away. Once a psyker is found, three Enslavers form
a dominating mental bond with the target and bring about a
sickening transformation. The host is distorted and twisted over
a period of days, falling into lethargy and finally becoming a
living warp portal, a pulsating arch of ruptured flesh which
permits the trio of Enslavers ingress into the material plane.
Once Enslavers have appeared on a world, they seek out and
transform more psykers so that more and more Enslavers appear,
thus often heralding the end of that world.
Enslavers can bind living creatures, including non–psykers,
to their will, using them to defend their new masters and
attack any who have not been enslaved yet. While some few
have resisted or thrown off this awful shackle, most victims
are dominated for the remainder of their pitiful lives. Enslaved
subjects usually bear no outward appearance of their domination,
but after time the lack of proper care and nourishment leave
them sick and desiccated, though this could be a side effect of
their alien oppression.
Once an Enslaver infestation has begun, it is very hard to
stop; soon thousands of the horrific creatures are breaching
the Warp, binding millions to their will and dooming the
planet. While their presence is still a very rare occurrence in
this sector, those worlds which have seen Enslavers appear
are now often Exterminatus, as the Holy Ordos have had
no other recourse but to unleash unrelenting death on the
planet. Only by catching the initial enslavement is there much
hope for stopping an Enslaver Plague from claiming a world.
The Enslavers were famously involved in a terrible conflict that proceeded the current war on Protasia. When the planetary governor planned secession and kept the tithe of psykers from the Black Ships, rogue psykers became vessels to bring the Enslavers into reality. The fleshy portals poured forth an army of Enslavers, who quickly took over the majority of the planetary population. Only the intervention of the Grey Knights, Battlefleet Calixis and other factions were the xenos put down.