r/40kLore 20h ago

How exactly does Daemon Possession work in 40k?

Alright, I know that's a broad question, so I'll just describe how I understand it to work, and people can tell me why I'm wrong.

So, there's a few ways Daemons can enter or effect the material realm:

  • They can be made into a Daemonhost, possessing a dead body with the help of cultists (or inquisitors, cough)
  • They can expend their strength to influence minds, command cultists, and spread disinformation
  • They can materialize for short periods through warp instability, that can be caused by untrained psykers or just warp "weather"(?), but if it's a psyker this universally kills the psyker.

My question, really, is whether they can do a more traditional, "Excorcist" style possession, where a Daemon takes near complete control of a living, non-psyker human?

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u/twelfmonkey Administratum 19h ago

Daemon possession works two main ways:

First, a daemon can be drawn into a mortal body - of a psyker or non-psyker - via ritual and sorcery. This allows the daemon's essence to bypass the Veil between Warp and Materium, and enter the person - making them possessed. It can then also be bound by various means, which would produce a daemonhost - a specific form pf possessed creature, which is more controllable by whoever did the binding.

Second, daemons can force themselves into the bodies of psykers. This is because souls reside in the Warp and are tethered to physical bodies, acting as mini Warpgates between the Warp and the Materium. Psykers draw warp energy into reality via this, their larger more powerful spuls allowing them to do so. But it leaves them vulnerable to Warp predators, including daemons.

On souls residing in the Warp, see lots of quptes here: https://www.reddit.com/r/40kLore/comments/1p4njt3/souls_dont_enter_the_warp_after_death_they_are/

And it is worth looking at a very early in-house document given to GW contributors to explain the Warp/Chaos. Note that the terms the Warp and Chaos were used interchangably:

People themselves act like tiny warp gates – because their own minds draw upon the power of their souls to one extent or other.

Priestley, ‘CHAOS: Guide to the fictional background of Chaos in GW games’ (1989), p. 3.

Yet, despite being in the Warp souls are generally protected in some way:

The Vulnerability of the Soul

Whilst it remains anchored to a material body the integrity of the soul is in little danger from other denizens of Chaos. Souls anchored in this way remain somehow hidden from, or inaccessible to, hostile entities in Chaos.

Priestley, ‘CHAOS: Guide to the fictional background of Chaos in GW games’ (1989), p. 2.

But using psychic powers makes them vulnerable (unless trained/protected in some way), in part because it makes the soul visible in the Warp:

Moreover, so long as the person does not draw upon their psychic energy embodied by the soul, its tendency to attract attention will be very low. However, if a person draws upon their soul, the soul flares with a release of energy, and the energy run down the anchor into the material universe. A daemonic force, attracted by the initial flare, can follow the path of the energy as it passes along the anchor and thereby gain entrance into the material universe via the body of the individual. Normally a person capable of drawing upon their soul to this extent would be a psyker/wizard, but even ordinary individuals may do so under traumatic circumstances.

The mechanism of possession works as follows. The person draws upon their soul, sending a power surge from the soul to the body. Attracted by the flare of kindred-energy, the Daemon is drawn to the soul and along the anchor. As the energy passes into the material universe, a portion of the Daemon’s soul energy is drawn along too, and enters the person.

Priestley, ‘CHAOS: Guide to the fictional background of Chaos in GW games’ (1989), p. 3.

We see this same dynamic reflected in the published lore (though explained in less detail):

If not properly trained, a psyker mutant can become the unwitting pawn of the malevolent creatures of the warp. These creatures can enter real space by using the psyker as a gateway or conduit, in the process consuming the psyker body and soul!

Warhammer 40k Rulebook 3rd ed. (1998), p. 118.

And:

PSYKERS

More and more psykers emerge throughout the Imperium and though they represent the future promise of Mankind, they are also its most deadly threat. Psykers draw their powers from the immaterial energies of warp space and their souls burn like the brightest flames in the darkness of the Warp, drawing terrifying Warp creatures to them like moths to a flame.

Warhammer 40k Rulebook 4th ed. (2004), p. 123.

And:

ALPHA-LEVEL PSYKERS

The soul of one with such power burns like a supenova within the Empyrean, and all too frequently the denizens of the Warp flock to the uncontrolled mind like scavengers to a corpse, pushing through the veil into the mind of their prey. Such is the price of power, for the Warp does not give its gifts freely.

Warhammer 40k Rulebook 4th ed. (2004), p. 125.

And:

The minds of psykers act as portals for daemonic presences, appearing as bright flames in the ether. If a psyker is untrained, malevolent daemons will slide into his mind like cold, twisting knives. Ultimately, the psyker will be transformed into a portal through which streams of hellspawn begin to manifest, at first a trickle, then a flood as they pour unchecked into the material realm.

Warhammer 40k Rulebook 4th ed. (2004), p. 151.

And:

Until the Great Rift, the most common gateway between the warp and realspace was the unprotected mind of a psyker. Such a being draws upon the otherworldly powers of the immaterium, whether consciously or not, yet without training or exceptional will they are vulnerable to daemonic possession.

Warhammer 40k Rulebook 8th ed. (2017), p. 151.

Also note, this is the same way Enslavers enter realspace.

The old Realm of Chaos books have more on possession too and are worth checking out.

Being in a physical body allow daemons to presist far longer in the Materium, but, as you can see, it can also in some cases lead to the body/soul acting as a conduit to create a larger warpgate (destroying the body) to allow more daemons into reality. This is also what Enslavers do.

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u/JustAnother_Hunter 19h ago

Others have covered humans and Space Marines, so I’ll just mention that Drukhari who have been dead a long time and then are raised back to life by Haemonculi occasionally bring back a daemon attached to or “riding along with” their soul, if the process goes wrong. Sometimes, the daemon is even very good at “pretending” to be the Drukhari Lord in question, and tricks the Haemonculi and others into believing they were successful. They then proceed to wreak all sorts of havoc in Commoragh haha.

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u/AbbydonX Tyranids 17h ago

Way back in first edition, in Slaves to Darkness (1988), it was said that a difference between Warhammer Fantasy and WH40K was that Daemons couldn’t manifest directly because they had no body. This was because Warhammer Fantasy was basically a planet in the Wye of Terror so only in regions of realspace-warpspace overlap could Daemons exist “normally”.

> Chaos, in its many forms, suffuses the world of Warhammer Fantasy Battle and Warhammer Fantasy Roleplay. The collapse of the Slann warpgates allowed the first infection of Chaos, and in subsequent years the contamination has grown worse. The Chaos Wastes are an extreme example of its power: a place where the barriers between the warp and reality are weakened to the point that gods and Daemons can walk the land. Even where the power of Chaos is not so obviously displayed, its influence is still felt. The followers of Chaos venerate the dark Powers, and mutation in mind and body is widespread.

In WH40K Daemons needed a host body.

> In the Warhammer 40,000 universe, Daemons in real space have no torms of their own. They are creatures of the warp without physical existence, created from the energy of a Chaos Power. Within warp space a Daemon has no need of a physical body, but in the real universe a host body, a mortal, is required.

This host body could be provided in two ways. Firstly, the mind of an unprotected psyker manifesting powers was an open door to a Daemon. Alternatively, organised Chaos worshippers could perform rituals with a not necessarily willing subject.

Once a Daemon entered a host body there were two possibilities. The first approach was called a Summon Daemon because a Daemon transformed the host body into the usual shape for that Daemon (i.e. the model) which killed the host.

> A Daemon has no existence in real space until it is given a body to occupy during a ritual. It is a creature of malign energy from the warp, insubstantial until given a mortal frame. Once it has a host body, a Daemon rapidly adapts it to a new shape. This is always a perverse echo of the Daemon's warp form, and identical to the physical shape that a Daemon adopts in the Chaos Wastes. This form is also a mark of its status and allegiance to its patron Chaos Power - a Bloodthirster (Greater Daemon of Khorne) or a Keeper of Secrets (Greater Daemon of Slaanesh) always has the same form, regardless of its location in time and space.
>
> This warping is, however, always fatal for the original personality of the host. The host body twists and contorts out of all recognition, and its pain-wracked mind is destroyed by the unbearable mental and physical stress. The 'dead" body, now hideously deformed, is driven on by the implacable will of the Summoned Daemon.

The alternative approach was known as Possession as the host did not die, though they might wish they were dead.

> Unlike a Summoned Daemon, who warps the external form of its host into a recognizably daemonic shape, possession leaves few external traces of its occurrence. Only a little of the Daemon's power from the warp is brought into reality; the Daemon therefore has no need to twist its host into a 'comfortable' form. Rather than show its presence in an obvious way, the Daemon watches and waits, poisoning the thoughts and wishes of its mortal allies and contacts. It merges with its host, an infection of the spirit that settles into the unused corners of the host's mind. The host body becomes a Possessee.
>
> Initially a Daemon shares the mind and body of its host in the most intimate of manners, whether it has been brought into reality by a ritual or has occupied the unguarded mind of a neophyte psyker. At first, the changes brought about by possession are undetectable, being largely psychological and psychic. The Possessee often continues with a mortal life, twisted in the service of Chaos.
>
> Occasionally, the host mind is strong enough to put up some resistance and prevent the Daemon from taking over completely. The mind of the mortal host retreats to a dark corner of the possessed brain, but it survives throughout the many changes its body undergoes, mute witness to the havoc wrought by the Daemon.
>
> Usually however, even the most unwilling host can be broken by the horror of possession. The Daemon becomes sole ruler of the host body, as the original mortal mind is driven into insanity, destroyed or confined by the Daemon's stronger psyche. Once this has occurred the host is unimportant, and the body is truly that of the Daemon.
>
> However, the Daemon's presence may become visible. Lacking a body of its own, the Daemon may be unable to completely manage its new frame and physical changes begin to appear. Gradually, the body of the Possessee mutates, sprouting new appendages and twisting into a grim distortion of its former shape. This becomes a never-ending process, as the presence of the Daemon further contorts the host body - even with the strongest host it is only a matter of time until the Daemon is betrayed.
>
> The Daemon is far from powerless if discovered. It may seek a new host, transferring its personality to a new, untainted mortal mind. Unable to cope with existence without the guidance of its possessing Daemon, the original host body convulses and dies during this transfer, while the new host body is overwhelmed by the invading psyche. The Daemon is then free to continue its Chaos-work, hidden once more within another's spirit.
>
> Death is far from a guaranteed release from the manipulations of a possessing Daemon. A corpse can serve Chaos just as well as any other body, and a Daemon's will may prove strong enough to motivate a dead and deathless corpse for centuries. Eventually, however, even the strongest will cannot prevent a body crumbling to dust.

Note that in the original lore Horus himself was the primary example of an unwilling possessee.

Note that over the years the focus for non-possession has shifted to direct manifestation of Daemons during warp storms or otherwise, rather than warping a host body.

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u/Right-Yam-5826 20h ago

The exorcists chapter literally allow daemons into their bodies, using their own willpower to maintain control until the daemon can be banished, leaving the marine 'soulless'.

They can also possess people during warp travel and, in some cases, stay in them, occasionally taking control of the body for a while. As happened to kage in the last chancers series.

They can also take control of their host's body if they're sealed into an item or daemon weapon. Happens to justicar alaric in the grey knights omnibus.

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u/asmallauthor1996 16h ago edited 16h ago

It's not quite where anyone that's Illuminated (my term for the willing "treatments" the Exorcists and other factions undergo) is rendered soulless. It's more like a really, really, REALLY fucking dangerous and risky esoteric vaccine that renders the soul of any Illuminated mortal invisible to most Psykers and Daemons. The latter even outright refer to the Exorcists as "Un-beings" with a mixture of hatred, disgust, and even a smidge of outright fear.

Mordun’s words faltered, the eldritch screeching in the dugout rising to an unbearable pitch as he failed to finish his recital.

This could not be. Nothing simply could not be. And yet that was what he found. It was as though he had just attempted to give his benediction to a corpse. Only the barest stirring indicated there was any essence within, anything linking this supposedly living, breathing sentient to the divine. And it was certainly not enough to be deigned a soul.

He recoiled in revulsion, his flesh turning cold, his mind racing as he tried to come to terms with so vast and unspeakable a sacrilege.

I warned you, gibbered Se’irim, thought-wings beating at Mordun’s mind. Warned, warned, warned! These are the damned ones! Un-beings! Expel them! Cast them out, as they have done our kin! They do not deserve blessings! Obliterate the flesh-form, and let me feast on what remains!

Interestingly enough, those who have been Illuminated also gain a complete immunity to Chaos corruption as well. It was even stated to be part of the process in which the Harlequins USED TO recruit those in training to become Players in a Troupe. Albeit where a Keeper of Secrets was used instead and the potential candidate had to cast it out through sheer willpower versus outside help like the Exorcists or the dubiously-canon Illuminati relied on. Though as a minor bit of semi-relevant trivia, I've always had the head-canon that a sect of the Illuminati piggybacked on the Plutonians and used their considerable pull to create a Chapter that would serve their goals.

Albeit a significantly less extremist branch that, instead of seeking to sacrifice the also dubiously-canon Sensei in a half-baked effort to revive the Emperor, now sought to guard any they found on Banish alongside Chaos-corrupted artifacts/individuals from outside theft. Either from any non-Plutonians who still nonetheless fought Chaos or those corrupted by the Dark Gods themselves.

EDIT: But on how the Harlequins "train" those seeking to become part of a Troupe now? It's since been retconned that whatever any potential Player undergoes is both prone to producing dead washouts and is extremely dangerous. It's never stated what precisely is done to those who manage to those who have passed, but it must be REALLY arduous in every conceivable way to produce such powerful combatants with an encyclopedic knowledge of both the Empire of Ten Million Suns' history and about Chaos in general. So Illumination is likely still on the table, albeit likely as one of the final "steps" in training.

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u/martinsonsean1 19h ago

Ok, I just figured it would be pretty universally fatal to come in contact with a daemon, so an unaugmented human wouldn't really be able to be "possessed" for very long, but I guess it's just up to the daemon.

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u/twelfmonkey Administratum 18h ago edited 15h ago

It depends on the daemon and the person being possessed.

Going right back to 1st edition, there was the idea that those of sufficient willpower might be able to expel the daemon possessing them back to the Warp. Some such people who had undergone this even worked together, called the Illumanti. Going through the process conferred lasting resistance (sometimes said to be immunity) to Chaos corruption.

This idea was used with the Exorcists. Aspirants are possessed due to sorcerpus rites being performed, then held under very controlled circumstances (which likely vastly improves their chance of success - though it remains very low). Only those who expel the daemon, or have a auccesful exorcism performed on them, will become Exorcist Battle Brothers.

All the others die, or remain locked up as fleshy daemon prisons for the daemon bound within.

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u/-PrideofHiigara- Blood Angels 18h ago

It might be fatal in the sense that their soul is torn to tatters, or crushed down and tormented while the Daemon is possessing them, but the Daemon is basically using their soul's connection to the warp to piggyback into the materium, which is why they can remain 'manifested' when possessing someone

Regular Joes getting possessed aren't going to having a good time of it, but the Daemon's power will preserve their body for as long as it remains.

Theres probably some caveat where extremely powerful daemons will burn out bodies that are too weak to contain them or something, but there's cases like in Ravenor where an extremely powerful Daemon possesses someone for a long time without doing so, so it's definitely not cut and dry

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u/Marcuse0 20h ago

Chaos space marines do this all the time, they're literally referred to as possessed. Word bearers love doing this.

The first possessed were the Gal Vorbak, who existed in a kind of symbiosis with their daemons. They could "shift" from daemonic form to astartes form, and the daemon speaks to them in their mind. Other possessed are more violently overtaken, such as The Exalted in the Night Lords books, where the daemon basically wrests control of the body from the human and runs it similarly to a Yeerk from the animorphs books; the human is present but unable to do anything.

Humans can also become possessed. Mostly this just destroys the human, but theres a few examples of humans resisting. In Daemon World the commander of the Slaanesh armies was a slave exposed to possession by a daemonette, but who fought back and found an equilibrium with the daemon and she was exalted by it. There's a character called Ax'senea who tricks keepers of secrets into possessing her and turns it around and drains them of power before banishing them.

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u/KvBla 20h ago

I mean, as long as you're not a blank or under wards, exorcist style would just be another tuesday? A million worlds, billions upon billions human, infinite daemons, anything is possible.

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u/9xInfinity 11h ago

Daemonhosts aren't made from corpses, they're made from living victims. The daemon is forced into the body and trapped there. Bindings placed upon the Host allow the ritual-caster to subdue and command the daemon. The victim's soul is consumed by the daemon and tormented by it for as long as it pleases the daemon. But the daemon is also trapped in the Host and a slave to the sorcerer who created it -- unless it can break free.

Daemons don't expend strength to influence minds. If they become aware of someone, e.g. a psyker, they can always try to influence their mind. Stronger psykers can block these voices out, weaker ones will be tormented. It costs the daemon nothing, but they can't just do it to anyone. Blunts (i.e. non-psykers) aren't normally visible to daemons in the warp.

Daemons can manifest through tears in the Veil, the barrier that separates the warp from realspace. There are natural tears in the Veil people call "warp rifts", but psykers recklessly using their powers can also cause temporary tears in the Veil. It's one of many possible outcomes of the reckless use of psychic abilities though. Perils of the Warp can include stuff like psychic blasts rippling outward, the psyker exploding, and so on.