Amidst the turmoil of the Horus Heresy, nine Adeptus Astartes legions rebelled against the Emperor, turning to the malevolent powers of Chaos to unleash havoc on humanity. Transformed by Chaos after being genetically enhanced by the Emperor, Chaos Space Marines stand as formidable adversaries.

Following the Heresy, the traitorous legions splintered into smaller warbands, launching raids into real space to sow terror. However, Abaddon The Despoiler managed to partially reunite these Chaos factions under his command, initiating the infamous Black Crusades. These Chaos warbands spread chaos and destruction across the galaxy, posing a dire threat to humanity's existence in the grimdark future of Warhammer 40k.

10 The Emperor’s Children

Pursuing Perfection In Every Aspect

• Notable Warbands: Flickering Blades, Cohors Nasicae
• Primarch/Leader: Fulgrim (Daemon Primarch)
• Allegiance: Slaanesh

The Emperor’s Children were fixated on perfection, excelling in various disciplines from combat to art. Their obsession, coupled with their corrupted gene father Fulgrim, led them to venerate Slaanesh, the chaos god of excess. Among the most warped and debauched of the traitor legions, they sought out twisted sensory pleasures.

Currently less active, The Emperor’s Children, if roused by Fulgrim, could pose a significant threat to humanity once more, notwithstanding their reduced presence in the galaxy.

9 The Night Lords

Spreading Fear Through Ruthless Campaigns

• Notable Warbands: Kreig Acerbus's Warband, The Bleeding Eye, The Exalted
• Primarch/Leader: Konrad Curze (Deceased)
• Allegiance: Many Follow No Faith, Some Follow Chaos Undivided

The Night Lords are infamous for utilizing fear as a potent weapon, instilling dread in their enemies. Once loyal enforcers for the Imperium, under the deteriorating sanity of Konrad Curze, they turned traitor during the Heresy, terrorizing all in their path.

Following Curze's demise, the Night Lords fragmented, dispersing as marauding warbands, spreading terror across the galaxy without a unified leadership.

8 The Alpha Legion

Engaged in Covert Operations

• Notable Warbands: The Shadowed Ones
• Primarch/Leader: Alpharius/Omegon (Deceased)
• Allegiance: Chaos Undivided

Operating in secrecy, the enigmatic Alpha Legion excels in undercover operations, infiltrating enemy ranks with hidden agents who strike at opportune moments. Dispersed into smaller factions post-Heresy, these warbands relentlessly promote chaos influence, supporting cultist uprisings throughout the Imperium.

Distinct from other Chaos Marines, the Alpha Legion avoids the mutating perils of the warp, focusing on inciting chaos cults to destabilize the Imperium.

7 The Thousand Sons

Masters of Warp Sorcery

• Notable Warbands: Brotherhood of Dust, Thralls Of Magnus, The Tizcan Host
• Primarch/Leader: Magnus The Red (Daemon Primarch)
• Allegiance: Tzeentch

Cursed by genetic instability, the Thousand Sons underwent a catastrophic transformation, rendering non-psykers soulless automatons. Led by the mighty psyker Magnus The Red, they wield formidable warp magic, harboring ambitions of unraveling the mysteries of the Immaterium.

Despite their potent sorcery, the Thousand Sons remain relatively restrained in active engagements, prioritizing esoteric knowledge and psychic mastery over widespread conflict.

6 Death Guard

Agents of Nurgle's Pestilence

• Notable Warbands: Lords of Silence, The Pallid Hand, Harbingers, Bringers Of Decay
• Primarch/Leader: Mortarion (Daemon Primarch)
• Allegiance: Nurgle

Rampant in their chaotic activities, the Death Guard, under Mortarion's leadership, embrace Nurgle's decay and disease. Traitorous First Captain Typhus orchestrated the Death Guard's fall to Nurgle, fostering a relentless crusade of pestilence and death.

Despite their allegiance to Nurgle, internal strife and Mortarion's waning favor with the Chaos god have complicated the Death Guard's unified actions, affecting their efficacy in spreading Nurgle's blight.

5 Iron Warriors

Experts in Siege Warfare

• Notable Warbands: Dark Castellans, Shatter Corps, Steel Brethren
• Primarch/Leader: Perturabo (Daemon Primarch)
• Allegiance: Chaos Undivided

Masters of siegecraft, the Iron Warriors, under Perturabo's command, excel in summoning and binding daemons to their war machines, unleashing devastating force in battles. Perturabo led a formidable assault on Terra during the Heresy, nearly toppling the Imperium.

Contributing significantly to Abaddon's Black Crusades, the Iron Warriors' relentless warfare prowess and technological expertise make them a critical force within the Chaos factions.

4 The Word Bearers

Fanatical Disciples of Chaos

• Notable Warbands: The Flayed Hand, The Unspeaking Chapter, The Blessed
• Primarch/Leader: Lorgar (Daemon Primarch)
• Allegiance: Chaos Undivided

The first Space Marine legion to embrace Chaos, the Word Bearers, once loyal to the Emperor, turned to the dark gods after their faith was shattered. Proficient in psychic abilities and combat, they excel in subverting Imperial faith, drawing masses to Chaos worship.

With their potent psykers and unwavering devotion to the Chaos cause, the Word Bearers remain a formidable threat, eroding the Imperium's foundations through insidious means.

3 Renegade Chapters

Chaos's Continuing Influence Amongst the Astartes

• Notable Warbands: Red Corsairs, Astral Blades, Bloodborn, Crimson Slaughter
• Primarch/Leader: Various Chaos Lords
• Allegiance: Chaos Undivided, Individual Chaos Gods

Emerging from diverse Space Marine chapters, the Renegade Chapters epitomize chaos's unrelenting spread across the Imperium post-Heresy. Led by formidable Chaos Lords, these warbands sow chaos and destruction, aligning with various Chaos entities for power.

Fear-inducing groups like the Red Corsairs exemplify the enduring threat of renegade Astartes, perpetuating endless conflict and strife in the name of Chaos.

2 The World Eaters

Bloodshed and Carnage in Khorne's Name

• Notable Warbands: Foresworn, Karagar’s Rampagers, 66th Armoured Company
• Primarch/Leader: Angron (Daemon Primarch)
• Allegiance: Khorne

Dedicated to sowing chaos and bloodshed in the name of Khorne, the World Eaters epitomize unbridled violence. With the return of Daemon Primarch Angron, their ferocity and strength have surged, leaving a trail of carnage in their wake.

Angron's unstoppable combat prowess and a malevolent curse unleashed by the World Eaters have bolstered their ranks, solidifying their reputation as Khorne's favored instruments of destruction.

1 The Black Legion

Unified Forces of Chaos in the Eternal Conflict

• Notable Warbands: Bringers Of Decay, Hounds Of Abaddon, The Tormented
• Primarch/Leader: Horus Lupercal (Deceased), Abaddon The Despoiler
• Allegiance: Chaos Undivided.

Standing as the foremost threat among Chaos factions, the Black Legion, under Abaddon the Despoiler, spearheads the relentless Black Crusades, leaving a trail of destruction in their wake. Originally led by Horus, they have resurged under Abaddon, achieving significant victories against the Imperium.

Abaddon's strategic prowess and alliances with formidable entities have elevated the Black Legion to unparalleled power, making them a force to be reckoned with in the ongoing war against the Imperium.