Chaos Space Marines Lore: Horus, the Traitor Legions, the Eye of Terror and Abaddon's Black Crusades (Plus How to Start)

Chaos Space Marines are the Imperium's greatest nightmare: Space Marines who betrayed the Emperor ten thousand years ago and now serve the dark gods of Chaos. Bitter, ancient and twisted by the warp, they return again and again to drown the Imperium in blood.

Army guide, last updated November 4, 2026. Lore summarised in our own words from Black Library novels, codexes and community wikis. For game rules, use the official codex or the official app.

Chaos Space Marines in 30 seconds

The fall of Horus

Horus Lupercal was the Emperor's favourite son and Warmaster of the Great Crusade. After being gravely wounded on the moon Davin, he was brought to a temple where the Chaos Gods reached him and showed him a future in which the Emperor was worshipped as a god while his sons were forgotten. Horus turned, and he took half the Legions with him.

The nine Traitor Legions

• Black Legion (once the Sons of Horus): Abaddon's Legion.
• World Eaters: berserkers of Khorne, led by Angron.
• Death Guard: plague-ridden servants of Nurgle, led by Mortarion.
• Thousand Sons: sorcerers of Tzeentch, led by Magnus the Red.
• Emperor's Children: perfectionists turned excess-addicts of Slaanesh, led by Fulgrim.
• Night Lords: terror-raiders, sons of Konrad Curze.
• Iron Warriors: bitter siege masters, led by Perturabo.
• Word Bearers: the first true believers in Chaos, led by Lorgar.
• Alpha Legion: masters of spying and deception.

The Siege of Terra

The war ended at the gates of the Emperor's Palace. During the Siege of Terra, Horus lowered his flagship's shields and the Emperor teleported aboard. Horus was destroyed, but the Emperor was left near death and placed on the Golden Throne. The leaderless traitors retreated into the Eye of Terror.

The Legion Wars

Inside the Eye, the Traitor Legions turned on each other. In the Legion Wars, the Sons of Horus were nearly destroyed and their Primarch's body was stolen to be cloned. Many Legions shattered into smaller warbands loyal only to their own champions. Time flows strangely in the Eye, so some traitors who fought in the Heresy are still alive today.

Abaddon and the Black Crusades

Ezekyle Abaddon, once First Captain of the Sons of Horus, rejected the Chaos Gods' favour for a time and rebuilt his Legion as the Black Legion. He took the title of Warmaster and launched the Black Crusades, massive invasions out of the Eye of Terror. His Thirteenth Black Crusade finally broke the fortress world of Cadia, helping tear open the Great Rift that split the galaxy in two.

Life as a traitor

Chaos Space Marines chase power and glory. Those who please the gods receive "gifts": mutations, daemonic weapons or even daemonhood, becoming immortal Daemon Princes. Those who fail can be turned into mindless Chaos Spawn. Many warbands are pirates and raiders, while others are fanatics. Some are even former loyalist Chapters who fell much later, like the Red Corsairs of Huron Blackheart.

Famous traitors

• Abaddon the Despoiler: Warmaster of Chaos, wielder of the daemon sword Drach'nyen.
• Huron Blackheart: once a loyal Chapter Master, now a pirate lord.
• Fabius Bile: a mad geneticist who works for no one but himself.
• Kharn the Betrayer: Angron's bloodthirsty champion.
• Ahriman: the greatest sorcerer of the Thousand Sons.

Black Library books to read

• Horus Rising (Dan Abnett): the start of the Horus Heresy
• The Talon of Horus (Aaron Dembski-Bowden): how Abaddon built the Black Legion
• Soul Hunter (Aaron Dembski-Bowden): the Night Lords trilogy

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Find them as Black Library paperbacks and audiobooks.

Collecting Chaos Space Marines: a quick guide

Elite and aggressive, with daemonic allies and brutal close-combat units. Start with: a Chaos Space Marines Combat Patrol or the Christmas Battleforce.

Painting tip

Black Legion black and gold is forgiving; add bone, red and rusty metal for a grim look.

New to the hobby? Start with our Warhammer beginner's hub, and see the other army guides.