Let the Galaxy burn!
~ Horus Lupercal
Death to the false Emperor!
~ Codex - Chaos Space Marines Page 3.

Chaos Space Marines (also called Traitor Marines, Chaos MarinesTraitor Legionnaires and Heretic Astartes) is the term used to describe the many heretical Space Marines that betrayed the Emperor of Mankind and became servants of the Chaos Gods. They are part of what might be considered the more villainous race in the Warhammer 40k universe, alongside the Dark Eldar, Orks, Necrons and Tyranids, and part of the Forces of Chaos, which also include demons and lesser humans. Chaos Space Marines come in many forms and tend to have cults of both human and xenos followers. Depending on the philosophy of the legion, they are deeply devoted to certain chaos deities, either one or all of them, but on rare occasions none of them.

Unlike many other factions within Warhammer 40,000, rather than being united under the umbrella of a higher figure or as loosely affiliated groups, they are fractious, fickle, refractory and prone to infighting amongst themselves. They are only truly unified in their will to survive, hatred of the Emperor Of Man and their desire to help Chaos become the ruling power of creation via acts of unspeakable evil. Only when the Warmaster of Chaos (The current being Abaddon) launches a new temporary Black Crusade will the vast majority of chaos warbands unify, for the sole purpose of wreaking as much havoc and destruction upon the galaxy as possible, the Imperium in particular. 

They are a playable army choice in Warhammer 40,000 and also serve in a highly antagonistic role in the related media. Chaos Space Marines are the rough equivalent of Warhammer Fantasy's Hordes of Chaos.


Chaos Space Marines draw their origins back to the 31st millennium. Back then, eighteen legions of genetically modified super-soldiers, the Space Marines, fought to unite the galaxy under the banner of the Imperium of Man, in a campaign that history later called the Great Crusade. The Emperor of Man Kind claimed that the intention of this campaign was to unite humanity under one banner, wipe out any xenos that threatened their dominion or survival and establish humanity as the ruling force in the galaxy. In truth, however, the Emperor knew about the existence of the Chaos Gods and the dangers they posed. His secret agenda was to their install the principal of the Imperial Truth - an atheistic doctrine, which would turn humanity away from the elements that served as the Chaos Gods power source thus eradicating them once and for all.

Perhaps fearing the eventual result, Khorne, Nurgle, Slaneesh and Tzeentch, as well as the lesser gods of chaos stopped their own conflicts to interfere with the works of the Emperor of Man. The first step was to scatter his genetically modified children, the Primarchs across the galaxy thus ensuring that the Emperor could not raise or teach them under his own philosophy from an early age. As such each of the Primarchs would face his own trial and tribulations before the Emperor rediscovered them, which in some cases sowed the first seeds of resentment against their father.  

Only once the Great Crusade was already underway, would the Chaos Gods seize their chance. Starting with the Emperor's disenfranchised son, the pious Lorgar Aurellian, who became disillusioned with his father following an incident in which the Emperor publicly humiliated both him and his legion, the Chaos Gods seduced Lorgar into Chaos-worship. When the Primarch undertook a pilgrimage, they showed him horrifying visions of the future under the Emperor and convinced him that without the aid of Chaos humanity would share the fate of the Eldar. Having won over a powerful leader and orator into their cause, the Chaos Gods' campaign to subvert the Emperor's faithful soldiers had begun.

After purging his Legion of all elements with any loyalties left to the Emperor, Lorgar sent his First Captain Erebus as an ambassador. Erebus, keeping his Legion's new faith a close secret, began organizing the Warrior Lodges, secretive fraternal orders within the Space Marine Legions that existed outside of the Legion's regimented and ordered structures. Though these were under the guise of providing brotherhood without rank, they were instrumental in fomenting sympathies and paving the way for the coming betrayal.

Erebus proved instrumental for setting the stage to the Horus Heresy after seeding the Warrior Lodges into a full half of the Legions and successfully engineering the fall of Horus into Chaos by stealing a powerful weapon known as the Anathame and giving it to a rebellious planetary governor who injured Horus with it. Desperate to save their leader Horus' troops were tricked into bringing him to the serpent's lodge, a group of supposed mystical healers who unknown to them were secretly chaos worshippers. Using this opportunity the Chaos Gods managed to convince the injured Horus to turn against the Imperium in exchange for healing him and he quickly rose to power as the leader of the Chaos forces.

The resulting conflict stretched across the known galaxy all the way to the throne world of Holy Terra consuming billions upon billions of lives, devastating countless worlds and ultimately leading to the Emperor's permanent interment upon the life support system known as the Golden Throne. In the end though Horus' rebellion cost him his life and his fellow traitor troops were forced to retreat into the realm of the Warp through the dimensional rift known as the Eye of Terror in order to avoid the wrath of the vengeful Imperial forces. Never the less a new deadly enemy had been created, from amongst humanities own ranks.

After the Horus Heresy

For the next 10,000 years, the fractured chaos legions would periodically emerge from the warp to wage war against the Imperium. Their lives unnaturally prolonged and their bodies and minds twisted thanks to otherworldly energies of the Warp and the daemons that live there. In their most recent endeavor, the 13th black Crusade, the new Warmaster of Chaos Abbadon the Despoiler managed to destroy the Imperial Fortress world of Cadia, an event which allowed the energies of the warp to spill into the material world and quite literally split the Imperium and the galaxy at large in half. Imperial forces have since retaliated by launching a counter-crusade to push back the onrushing forces and seize the two remaining space paths to the other side of the galaxy, all while the chaos forces use the opportunity to harass and harry them as well as devastate any worlds in their path.

Known Chaos Legions

During the Horus Hersey, nine of the First-Founding Legions and their Primarchs turned against humanity and the Emperor, siding with Horus and the Chaos Gods. In the aftermath of the heresy, the majority of these legions divided into roaming warbands. Like their loyalist kinsman's newly formed chapters, some of these traitor warbands adopted new names and philosophies to differentiate from their parent legion. In subsequent years, a number of Space Marine chapters followed their former-brethren down the dark path, in exchange for the power and glory promised by the Dark Gods.

The following list comprises the known Chaos legions from the first founding: - 

  • The Black Legion
Legion number: XVI
Primarch: Horus. 
 Status: Deceased - soul destroyed by the Emperor during the Siege of Terra.
Current leader: Abaddon the Despoiler.
Religion: Most of the astartes from the Black Legion follow Chaos Undivided, meaning they worship all of the Chaos Gods and will give particular devotion to a single entity when the situation calls for it. That said, some legionnaires, especially those from other legions, are monotheistic and will follow only one God.
Additional notes: Was originally known as The Luna Wolves Legion. Changed their name to The Sons of Horus just before the start of the Horus Heresy. During the betrayal at Istaavan III, loyalist members of the XVIth legion readopted the title of Luna Wolves to signify their allegiance to the Emperor.
These are the most famous of all the traitor legions. Following Horus' defeat, they became a withdrawn legion, until Abaddon rallied the survivors under his leadership and promised to succeed where Horus had failed. His first step was to order his legionnaires to paint their armor black to mask their shame of Horus' failure, which in turn inspired their new name.
  • The Word Bearers
Legion Number: XVII
Primarch: Lorgar.
 Status: Alive - meditating deep within the depths of the Word Bearers homeworld.
Current Leader(s): The Dark Council.
Religion: The Word Bearers are staunch pagans of Chaos Undivided. They worship all of the Chaos Gods equally and never show favour to a particular deity.
Additional notes: The legion was originally known as the Imperial Heralds. When Lorgar took control of the legion, he renamed it the Word Bearers as a sign of his absolute devotion to the Emperor.
The XVIIth legion was the first legion to turn against the Emperor, following what they viewed as an unjustified humiliation and reprimand at the hands of the Emperor himself. Since the legion was always pious, many willingly accepted the Chaos Gods, who welcomed their devotion when the Emperor spurned it.
Ironically, before his fall Lorgar penned a book of reverence to the Emperor, which gave rise to the modern-day Imperial Cult.
  • The World Eaters
Legion number: XII
Primarch: Angron.
 Status: Alive - last seen during the First War of Armageddon. Defeated but not destroyed.
Current leader: N/A, legion divided into warbands.
Religion: The World Eaters are the acolytes of Khorne the God of Blood and War. The battlefield is their altar, and they have earnt themselves the nickname, Khorne Berserkers.
Additional notes: Were originally called the War Hounds, before the Emperor rediscovered Angron. The Primarch immediately renamed his new legion after his fallen comrades from the gladiatorial arenas on his homeworld.
They are formidable warriors who excel in hand to hand combat, willing to fight anyone and everyone, including each other.  
  • The Death Guard
Legion number: XIV
Primarch: Mortarian.
 Status: Alive - duelled Robute Guilliman at the climax of the Plague Wars.
Current leader: N/A, legion divided into warbands.
Religion: The Death Guard are the most adherents of Nurgle. Blessed by their deity to house plagues and diseases, they have mutated into what Imperial records now refer to as the Plague Marines.
Additional notes: Before Mortarian was found, the Emperor referred to the legion as the Dusk Raiders. Mortarian renamed them after his forces on his homeworld of Barabus.
  • The Emperors Children 
Legion number: III
Primarch: Fulgrim
 Status: Alive - returned to Istvaan III, where he fought the Venerable Dreadnaught Rylanor. 
Current leader: N/A, the legion divided into warbands.
Religion: Slaanesh, the Dark Prince of Excess corrupted Fulgrim, and then his legion. Where once they sought perfection in all things, they now seek carnal pleasure in all things. Their use of sonic weaponry has earnt them the name Noise Marines. 
Additional notes: This was the legion that the profaned, amoral scientist Fabius Bile came from. Indeed, some of Biles earliest experiments were on his own legion. Bile eventually left the legion to continue his sadistic experiments without restraint.
Fulgrim was the one responsible for Robute Guilliman's original death. He struck his former brother down with a poisoned blade. This forced Guilliman to remain locked in stasis until his resurrection at the end of the 41st Millenium.
Unknown to most, Bile managed to create a perfect clone of Fulgrim, who displayed loyalist affiliations. Bile betrayed his creation before any harm could be done. The Phonecian Clone as he was dubbed, is currently imprisoned within Trazyn the Infinite's collection. 
  • The Thousand Sons
Legion number: XV
Primarch: Magnus the Red.
 Staus: Alive - fought Guilliman on Luna, now heading an invasion force in the Stygius Sector.
Current leader: Various, several known bands exist.
Religion: As prominent magic users, it did not take long for the Thousand Sons to find favour with Tzeentch, the Changer of Ways.
Additional notes: The legion was left with no choice but to side with Chaos when Magnus broke a sacred taboo to warn the Emperor about his brother Primarchs betrayal. The Emperor sent the Space Wolves to bring Magnus in for questioning, but Horus tricked his brother into thinking this was an order of extermination. Magnus pledged his warriors souls to Tzeentch and since then they have followed him without question.
Following the Rubric of Ahriman, most of the legion are bodiless automatons, whose souls are now permanently bound to their power armor, now known as the Rubric Marines. 
  • The Iron Warriors
Legion number: IV
Primarch: Perturabo.
  Status: Alive - current location unknown.
Current leader: N/A, a civil war divided the legion creating various warbands.
Religion: Although classified as being part of Chaos Undivided, in reality, the Iron Warriors can be described as agnostic or deistic. Whilst they acknowledge the existence of the Chaos Gods, they do not worship them because, like their Primarch, astartes of the IVth legion hold no attachment to faith. They favour the materialistic gifts of science and technology over magic and blessings.
Demon Princes are very rare within this legion, and the Iron Warriors rarely works alongside demons.
Additional notes:  Although they seek conquest in all its glory, showing no mercy to enemies, the Iron Warriors have been known on very rare occasions to aid the forces of the loyalists against overwhelming odds.
In accordance with their philosophy, if an Iron Warrior astrate shows any signs of physical mutation he will be assessed. If the mutation is deemed too great, he will be terminated. If he is deemed salvageable, the affected limb will be amputated and replaced with a cybernetic replacement.
  • The Night Lords
Legion number: VIII
Primarch: Konrad Curze aka The Night Haunter.
 Status: Deceased - allowed himself to be killed by an Imperial Assassin, shortly after the Heresy. 
Current leader: N/A. legion has divided into several warbands.
Religion: Officially, they are classified as being part of Chaos Undivided. In reality, however, the Night Lords are an oddity amongst the Chaos Space Marines. Unlike the other legions who follow Chaos to varying degrees, astartes from the VIIIth legion neither acknowledge or worship the Chaos Gods at all. Indeed, they actively mock their fellow traitors for their loyalties to the immaterial. 
Dedicated to their principals of fear and terror above all other things, their actions aid the cause of Chaos as a side-effect. Despite clear evidence to the contrary, the Night Lords legion remains predominantly atheist. Demon Princes and demonic summoning is the exception in this legion, rather than the rule.
Additional notes: One of the darkest legions ever created, even during their time as loyalists this legion had a fearsome reputation for savagery and instilling absolute fear into their enemies.
Was the first legion to officially leave the Emperor's service and turn renegade. This happened prior to the Horus Heresy, though, when the conflict began, they became allies of Horus.
  • The Alpha Legion
Legion number: XX
Primarch: Alpharius Omegon - was actually twin Primarchs, one named Alpharius, the other Omegon.
 Status: One or both deceased, contested.
Rogal Dorn killed one of the brothers, reportedly Alpharius, above Pluto. Guilliman is said   to have killed the other Primarch after the Heresy, but this remains unconfirmed.
Current leader: Unknown. Various warbands exist but it is possible that they all answer to a hidden overlord.
Religion: Noted for their use of cultists, the Alpha Legion worships Chaos Undivided.
Additional notes: Are one of the few legions that did not move towards the Eye of Terror after Horus' defeat and maintain an ongoing presence in real-space.
Several sources have indicated that although they aid the Forces of Chaos, the Alpha Legion (or at least the first generation) seeks to destroy the Chaos Gods in its entirety, and do in-fact consider themselves loyalists. Before his "fall" the Alpha Legion Primarch, Alpharius received a vision in which he saw the twin fates of the galaxy. In one version, the Emperor won the Heresy but Chaos ultimately triumphed as a result of the subsequent turmoil. In the other vision, Horus defeated the Emperor but then lead humanity to the point of extinction, resulting in the death of the Chaos Gods. After receiving his visions, Alpharius is reported to have said these words, "Whatever I do now, I do for the Emperor!"


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