Chaos Space Marines: Warhammer 40K Lore Guide

Ten thousand years ago, half of the Emperor's Space Marine Legions turned their guns on the Imperium they had built. They burned worlds they had once liberated, butchered brothers they had once fought beside, and marched on Terra itself to drag the Emperor from his throne. They failed. But they did not die. Driven into the warp-soaked hell of the Eye of Terror, where time runs strangely and the Dark Gods walk, the traitors endured. Today they still wage what they call the Long War: a crusade of vengeance against the Imperium that betrayed them, or so they tell themselves.

These are the Chaos Space Marines, the Heretic Astartes. They are every bit as strong, as fearless and as superbly trained as their loyalist cousins, but they have been remade by ten millennia of hatred, mutation and dark pacts. Some are idealists who still believe the Emperor was a tyrant. Some are pirates and warlords who simply refuse to kneel. Many have given their souls to Khorne, Nurgle, Tzeentch or Slaanesh. Of all the Warhammer 40K factions, they are the setting's great tragic villains: the dark mirror of humanity's finest warriors.

Chaos Space Marines at a Glance

Aspect	Detail
Also Known As	Heretic Astartes, Traitor Marines, the Traitor Legions
Origin	The nine Space Marine Legions that sided with Horus during the Horus Heresy, plus renegade Chapters that fell later
Leader	Abaddon the Despoiler, Warmaster of Chaos and master of the Black Legion
Home	The Eye of Terror, the Maelstrom and countless daemon worlds; since the Great Rift, half the galaxy
Allegiance	The Chaos Gods, either together (Chaos Undivided) or to one god alone
Signature Wargear	Ancient power armor, boltguns, chainaxes and daemon-bound weapons
Defining Trait	Transhuman warriors corrupted by hatred, mutation and pacts with the Warp
Rallying Cry	The Long War: vengeance against the Emperor and his Imperium

The Horus Heresy: How Angels Fell

At the height of the Great Crusade, the Emperor of Mankind named his favored son, the Primarch Horus Lupercal of the Luna Wolves, as Warmaster: commander of all the Imperium's armies while the Emperor returned to Terra. It was the greatest honor in the galaxy, and it became its greatest tragedy. Wounded on the moon of Davin and manipulated by the Chaos Gods and their mortal agents, Horus came to believe that his father was a false god who would cast his sons aside. He chose rebellion.

He did not rebel alone. Nine of the eighteen known Legions followed him into treason, some through faith, some through grievance, some through the slow rot of corruption. The Word Bearers had already turned to the Dark Gods. The Emperor's Children were seduced by Slaanesh. The World Eaters and Night Lords had long been tolerated as necessary monsters. The Iron Warriors nursed old resentments. The Death Guard, Thousand Sons and Alpha Legion fell for reasons as complex as the Primarchs who led them.

The war that followed engulfed the galaxy. It began with the massacre of loyalists on Isstvan III and the Drop Site Massacre on Isstvan V, raged across thousands of worlds, and ended with the Siege of Terra. In the final hours, the Emperor boarded Horus's flagship and slew his son, but he was mortally wounded and has been entombed on the Golden Throne ever since. With the Warmaster dead, the Traitor Legions broke. Hunted by the loyalists during the Great Scouring, they fled into the Eye of Terror, a vast wound in reality where the Warp spills into real space.

The Eye of Terror and the Long War

Inside the Eye, the Traitor Legions did not rest. Time flows unpredictably there: some warriors who fought at the Siege of Terra are still alive in the 41st and 42nd millennia, having experienced only centuries of subjective time. Daemon worlds shaped by the whims of the gods became their fortresses, and the Legions quickly turned on each other in the Legion Wars. The Sons of Horus were broken, and the Emperor's Children stole the Warmaster's corpse so that the twisted geneticist Fabius Bile could try to clone him. The World Eaters shattered into bands of berserkers after the battle of Skalathrax. Within a few centuries, the great Legions had mostly dissolved into warbands: a few hundred warriors, or a few dozen, following whichever champion was strongest.

Their war against the Imperium never ended. Chaos Space Marines call it the Long War, and its fighters span every kind of motivation. Some are true believers who still preach that the Emperor was a tyrant. Some are reavers who raid human worlds for slaves, weapons and gene-seed. Some chase the favor of the gods in pursuit of the ultimate reward: daemonhood. For more on the four powers behind it all, read our complete guide to the Chaos Gods.

Abaddon and the Black Crusades

The man who reforged the traitors into a threat that could rival the Heresy was Ezekyle Abaddon, once First Captain of the Sons of Horus. Disgusted by the theft of his Primarch's body, he destroyed Bile's clone, burned the Warmaster's remains and renamed his Legion the Black Legion, its armor stripped of the old sea-green and painted the black of mourning and shame. He then set about a task no one else had managed: uniting the bickering warbands under one banner.

Abaddon wields the Talon of Horus, his gene-father's lightning claw, and Drach'nyen, a daemon blade of terrible power. He has refused to bow fully to any single god, preferring to use them all. Over ten thousand years he led thirteen Black Crusades out of the Eye of Terror, each one seemingly a failure, each one in fact advancing a hidden plan. The Thirteenth Black Crusade, at the end of the 41st millennium, achieved what the others had prepared: the fortress world of Cadia, the Imperium's gatekeeper to the Eye for millennia, was destroyed.

The fall of Cadia was followed by the opening of the Great Rift, a scar of warp storms that split the galaxy in two and cut off the Imperium Nihilus from the light of the Astronomican. The Imperium answered with the return of Roboute Guilliman and the Indomitus Crusade, but the traitors now have open roads into the heart of the Imperium. In the current era, Chaos Space Marines raid, conquer and corrupt on a scale not seen since the Heresy.

The Traitor Legions

Nine Legions followed Horus into damnation. Five of them remain part of the Chaos Space Marines army; four have been so thoroughly transformed by a single god that they now fight as separate forces with guides of their own.

Black Legion (formerly the Sons of Horus)

Abaddon's own Legion and the closest thing the traitors have to a central power. The Black Legion recruits from every warband that swears allegiance to the Warmaster, so its ranks mix veterans of the Heresy, renegades from more recent eras and mortal cultists by the billion. They fight for Chaos Undivided, honoring all four gods together.

Night Lords

The sons of Konrad Curze, the Night Haunter, raised on the lightless, crime-ridden world of Nostramo. Curze believed that only fear could keep order, and his Legion became masters of terror: flaying victims, broadcasting their screams across vox-channels and striking from the dark on jump packs. Curze foresaw his own death and allowed an Imperial assassin to kill him. Many Night Lords still claim they serve no god at all, only their hatred and their appetite for terror.

Iron Warriors

The Legion of Perturabo, the bitter genius from Olympia, was used as a siege tool throughout the Great Crusade: endless grinding assaults with little glory and heavy losses. That resentment made them traitors. The Iron Warriors remain the masters of siegecraft, fortification and daemon-engine warfare, cold engineers whose battle cry is "Iron within, iron without." Perturabo now rules the daemon world of Medrengard as a Daemon Prince.

Alpha Legion

The last and most mysterious Legion, led by the twin Primarchs Alpharius and Omegon. The Alpha Legion specializes in infiltration, misdirection and cultist networks hidden inside Imperial worlds. Even their reasons for siding with Horus remain debated, and their warriors traditionally answer to the name "Alpharius" to confound their enemies. Their emblem is the many-headed hydra.

Word Bearers

The first Legion to fall. Rebuked by the Emperor for worshipping him as a god, the Primarch Lorgar turned his zeal toward the true gods of the Warp, and his Legion seeded the corruption that became the Heresy. Today the Word Bearers are a church militant of Chaos, led into battle by Dark Apostles who preach the gods' glory and summon daemons to their side. Lorgar himself ascended to daemonhood and withdrew into the Eye of Terror.

The four god-bound Legions

Four Legions gave themselves entirely to a single Chaos God and were transformed beyond recognition. Each is its own army with its own lore:

• The Death Guard: Mortarion's plague-ridden Legion, sworn to Nurgle after a voyage through the Warp turned into a nightmare of disease. Bloated, rotting and almost impossible to kill.
• The Thousand Sons: Magnus the Red's sorcerers, servants of Tzeentch. Most of the Legion was reduced to dust sealed in armor by the Rubric of Ahriman, a spell meant to save them.
• The World Eaters: Angron's berserkers, driven by the Butcher's Nails in their skulls to worship Khorne through endless slaughter.
• The Emperor's Children: Fulgrim's perfectionists, who turned their pursuit of excellence into a pursuit of sensation in the name of Slaanesh.

Renegade Chapters and Warbands

Not every Chaos Space Marine fell ten thousand years ago. Throughout the history of the Imperium, Chapters and individual battle-brothers have turned renegade: through pride, through politics, through despair, or because a Chaos cult whispered the right words at the right time.

The most infamous are the Red Corsairs. They began as the Astral Claws, a loyalist Chapter whose Chapter Master, Lufgt Huron, rebelled against the Imperium in the Badab War. Defeated and maimed, Huron fled into the Maelstrom, another great warp rift, and rebuilt himself as the pirate lord Huron Blackheart. The Red Corsairs now recruit from every disgruntled Marine who will join them, making them one of the largest renegade forces in the galaxy. Others include the Crimson Slaughter, once the loyalist Crimson Sabres, a Chapter haunted by the voices of the people they massacred.

Below the level of Legions and Chapters, the true unit of Chaos is the warband: a champion and the warriors bound to him by fear, loyalty or shared ambition. A warband might include Heresy-era veterans, renegades of a dozen former Chapters, cultists, mutants, and daemon engines. Every one is unique, which is a big part of the army's appeal for players and storytellers alike.

Marks, Mutations and the Path to Glory

The Chaos Gods reward those who serve them well, but their gifts are a double-edged blade. A champion who pleases a god may receive a Mark of Chaos: the Mark of Khorne grants fury in battle, the Mark of Nurgle supernatural resilience, the Mark of Tzeentch sorcerous power, and the Mark of Slaanesh unnatural speed and grace. Many warriors bear mutations: horns, extra limbs, armor fused to flesh, faces twisted into something inhuman.

This is the Path to Glory, and it has two endings. A champion who rises high enough may be granted daemonhood and reborn as a Daemon Prince, an immortal being of the Warp. One who fails, or who receives too many gifts, collapses into a Chaos Spawn: a mindless, mutating mass of flesh. Both fates are common, and both are part of the bargain every Chaos Space Marine makes. The gods' own servants, the daemons who fight alongside the traitors, are covered in our Chaos Daemons guide.

Warriors and War Machines of the Long War

Chaos Space Marines field the same core weapons as the loyalists, often ancient patterns lost to the Imperium, alongside weapons and engines that no loyalist would touch:

• Legionaries: the backbone of the army. Veterans of the Long War, often centuries or millennia old, wielding boltguns and chainswords.
• Chosen and Chaos Terminators: elite champions and their honor guard, clad in ancient Terminator plate.
• Possessed: warriors who have willingly allowed a daemon to share their body, their armor warped into claws, tentacles and fanged maws.
• Raptors and Warp Talons: jump-pack hunters who strike from above, a tradition inherited from the Night Lords.
• Havocs: heavy-weapon specialists who bring autocannons, lascannons and missile launchers to the battle.
• Obliterators: Marines infected with a techno-virus that fuses flesh and weapons into a single grotesque war machine.
• Cultists and Accursed Cultists: masses of mortal worshippers and mutants, thrown into battle as fodder.
• Helbrutes: Chaos Dreadnoughts, whose occupants have been driven mad by centuries entombed in an iron sarcophagus.
• Daemon engines: Defilers, Forgefiends, Maulerfiends and Heldrakes, war machines with bound daemons for hearts, forged by Warpsmiths and the Dark Mechanicum.

The leaders are just as varied: Chaos Lords commanding warbands, Sorcerers channeling the raw power of the Warp, Dark Apostles leading prayers to the gods, and Warpsmiths who bind daemons into their engines. When the traitors need even greater firepower, they call on their allies, the fallen Knight houses described in our Chaos Knights guide.

Chaos Space Marines and the Loyalists

The relationship between the traitors and the loyal Space Marines is the emotional core of Warhammer 40,000. They share the same Primarchs' blood, the same gene-seed and the same training. Loyalists see the traitors as the ultimate betrayal; traitors see the loyalists as deluded slaves of a corpse-god. Many Chaos Space Marines are older than the Chapters fighting them, and some still remember the loyalist Primarchs as brothers.

That shared origin also makes the traitors dangerous to the Imperium in a quieter way. Chaos warbands raid Imperial worlds for gene-seed to make new Marines, and they sow corruption in the hope that loyalist Chapters will fall as the Astral Claws did. Every renegade Chapter proves that the Heresy is not over; it simply continues one warrior at a time.

How Chaos Space Marines Play on the Tabletop

On the tabletop, Chaos Space Marines are an aggressive, flexible elite army. Like the loyalists, they rely on tough, expensive models, but their identity is built around risk and reward: the gods offer power at a price, and the army rewards players who are willing to gamble. You can dedicate units to Khorne, Nurgle, Tzeentch or Slaanesh to change how they fight, and you can mix fast assault elements, heavy firepower, daemon engines and cheap cultists in a way few other armies can.

The range is a mix of newer kits and older classics, which makes it a favorite of hobbyists who love conversions and kitbashing. If you want to build a unique warband with its own colors, mutations and backstory, there is no better army.

Chaos Space Marines FAQ

Who leads the Chaos Space Marines?

The closest thing to a supreme leader is Abaddon the Despoiler, Warmaster of Chaos and lord of the Black Legion. In practice, the Traitor Legions and warbands are fiercely independent, and Abaddon commands them only when his strength and reputation force them to follow, as during his Black Crusades.

How many Traitor Legions are there?

Nine: the Black Legion (formerly the Sons of Horus), Night Lords, Iron Warriors, Alpha Legion, Word Bearers, Death Guard, Thousand Sons, World Eaters and Emperor's Children. The other nine known Legions remained loyal to the Emperor, and two more were erased from the records before the Heresy.

What is the difference between Chaos Space Marines and Death Guard or World Eaters?

The Chaos Space Marines army covers the Legions and renegades who serve all the gods together or remain flexible in their allegiance. The Death Guard, Thousand Sons, World Eaters and Emperor's Children are Legions that devoted themselves entirely to one god; in both the lore and the game, they have become distinct forces.

Are the Black Legion and the Sons of Horus the same?

Yes. The Black Legion is the Sons of Horus, renamed by Abaddon after the Warmaster's body was stolen during the Legion Wars. Abaddon wanted to break with the failure of Horus, so he painted his Legion's armor black and gave it a new name.

Do all Chaos Space Marines worship the Chaos Gods?

Not consciously. Some, like many Night Lords and the Red Corsairs, claim they serve no god, only themselves. But anyone who lives in the Eye of Terror and wields the power of the Warp is touched by Chaos whether they admit it or not, and the gods are patient.

Continue Exploring

• Warhammer 40K Factions: Complete Guide to All 29 Armies — every army, its lore and how it plays
• Chaos Daemons — the gods' own servants, made flesh in the material world.
• Chaos Knights — fallen noble houses whose giant war machines march with the traitors.
• Space Marines — the loyal Astartes and the Chapters that still hold the line.
• Death Guard — Mortarion's plague Legion, sworn to Nurgle.
• Thousand Sons — Magnus the Red's sorcerer Legion, sworn to Tzeentch.
• World Eaters — Angron's berserkers, sworn to Khorne.
• Emperor's Children — Fulgrim's decadent perfectionists, sworn to Slaanesh.

For the rest of the setting, browse every guide in the Warhammer 40K lore hub, and give your warlord a suitably sinister name with the Chaos Space Marine name generator. To chronicle your own warband's Long War, Anima is free and runs in your browser with no account: a wiki, a timeline, and campaigns with a live DM screen.