🎲 The Setting
Factions & Enemies — A Table-Ready "Who's Who"
A scannable reference for your 40k one-shot. Skim before the game; flip to it mid-session when a player asks "wait, who are these guys again?" Keep it on the DM screen.
The one-sentence frame: In the 41st millennium the galaxy is one endless war. The Imperium of Man — a decaying, fanatically religious human empire of a million worlds — barely holds against demons, aliens, and traitors. It is "technically the good guys" only because every alternative is worse. In the grim darkness of the far future, there is only war.
PART 1 — FORCES OF THE IMPERIUM
These are the "good guys" (the term is doing a lot of work). They're zealous, brutal, and terrified — and they're who your players almost certainly are. A classic one-shot party is an Inquisitor's warband or a Guard squad: a handful of competent-but-mortal humans against impossible odds.
| Faction | What they are | The vibe at the table |
|---|---|---|
| Astra Militarum (Imperial Guard) | The Imperium's endless mortal army — ordinary humans with lasguns, expendable by the billion. The "trench infantry" backbone that wins wars by sheer attrition, not super-powers. | The everyman PC. Brave, doomed, and led by Commissars who shoot their own troops for cowardice. "We hold the line and most of us die for a reason." |
| Adeptus Astartes (Space Marines) | 7-foot genetically-engineered transhuman super-soldiers in power armor — the iconic poster-boys. Organized into ~1,000-strong Chapters. Few, elite, near-unstoppable. | The legend. If a Marine is in your one-shot it's a big deal — they outclass mortals so hard they're often best as an NPC ally or a single power-tier PC. |
| The Inquisition | The Imperium's secret-police god-cops. Inquisitors hunt heretics, mutants, daemons, and aliens with near-unlimited authority — they can requisition fleets or exterminate worlds on suspicion. | The perfect one-shot patron. An Inquisitor hands the party a mission and a warrant; their warband (assassins, tech-priests, psykers, hired scum) IS the party. |
| Adeptus Mechanicus (Tech-Priests) | The cyborg priesthood that worships the Machine God and hoards all technology. They chant prayers to repair tech and treat machines as holy relics — because the Imperium can no longer understand most of its own gear. | The party's engineer/medic-of-machines. Cold, half-robotic, speaks in binary cant. "The Omnissiah provides." Distrusts anything they didn't bless. |
| Ecclesiarchy & Adepta Sororitas (Imperial Church & Sisters of Battle) | The Ecclesiarchy is the state religion that worships the Emperor as a god; the Sisters of Battle are its militant warrior-nuns — power-armored fanatics with flamers and faith literally strong enough to deflect bullets ("Acts of Faith"). | Holy fire and zealotry. The Sisters are the Inquisition's iron fist against witches and heretics. "Burn the heretic. The Emperor protects." |
Ordinary citizen belief (the texture under all of it): A normal person knows three things — "The Emperor protects," worship constantly, and fear and hate the witch, the mutant, the alien, and the heretic above all. Curiosity is dangerous; "Blessed is the mind too small for doubt." Players quoting scripture and recoiling from anything strange = playing it right.
PART 2 — THE ENEMIES
The threats that make 40k 40k. Each gets the lore plus ▸ At the table — how it'd actually show up as the antagonist in a 3-4 hour one-shot. (Stat-block reskins live in the separate enemies guide; here's the who and why.)
Chaos — the enemy within and without
The great corruptor. The Warp is a parallel "soul-dimension" of raw emotion that powers FTL travel and psykers — but it's home to daemons and the four Chaos Gods, each born from a mortal feeling. Giving in turns you into a cultist, a daemon-thing, or worse. Chaos is the heretic next door.
| The Four Gods | Domain | Flavor |
|---|---|---|
| Khorne | Rage, blood, war, skulls | The Blood God. "Blood for the Blood God!" Mindless berserk slaughter. |
| Nurgle | Disease, decay, despair | The grandfatherly Plague God who "loves" you by rotting you. Cheerful, putrid, patient. |
| Tzeentch | Change, scheming, sorcery, ambition | The Architect of Fate. Plots within plots; the patron of sorcerers and liars. |
| Slaanesh | Excess, pleasure, obsession | The dark prince of indulgence taken past all limits. (Handle off-screen / PG-13 for the table.) |
- Chaos Space Marines: the traitor Astartes from the Horus Heresy — superhuman Marines who turned to Chaos 10,000 years ago and are STILL at war. The setting's signature heavy villains.
- Chaos Cultists: ordinary humans who secretly worship the Dark Gods — chanting, sacrificing, weakening reality from inside the Imperium.
- Daemons: entities spat from the Warp to butcher mortals — Bloodletters (Khorne), Plaguebearers (Nurgle), Pink Horrors (Tzeentch).
▸ At the table: The best beginner antagonist. Start with a cult hiding in plain sight (a social/investigation scene — who's the heretic?), escalate to robed cultists in a ritual fight, climax with a single Chaos Space Marine or summoned lesser daemon bursting through. Teaches saves and dread without needing alien rules. A Cult Fanatic preacher is a great first mini-boss.
Orks — the savage green tide
Fungal green-skinned brutes who live for one thing: a good fight. Crude, numberless, gleefully violent, and genuinely thrilled to die in battle. Their slapped-together tech works partly because they collectively believe it will (red ones really do go faster). Led by the biggest, meanest Nob present.
▸ At the table: Pure escalating combat and comic-menace. Open with cowardly Grots (knee-high runts who flee), build to a mob of Ork Boyz charging headlong, and cap it with a Nob boss. Forgiving for beginners — lots of weak bodies plus one clear, dumb, dangerous boss. Great for teaching action economy.
Tyranids — the all-devouring swarm
An extragalactic hive-mind swarm of bio-engineered monsters that strips a world of every scrap of biomass and moves on. Pure consumption — locusts crossed with Alien. No reasoning, no mercy, no negotiation; just hunger directed by a single will. Vanguard Genestealers infiltrate first.
▸ At the table: Horror-movie tension. Run Genestealers bursting from vents and ducts — fast, clawed ambushers that are deadly in numbers, not alone. Perfect for a creeping "something's hunting us in the dark" set-piece on a doomed ship or station. Let the dread build before the claws come out.
Necrons — the undying machines
Ancient skeletal robot-undead, an entire dynasty waking from a 60-million-year slumber to reclaim the galaxy they once ruled. Cold, methodical, near-unkillable — they get back up. Gauss weapons that flay matter atom by atom. Patient as a tomb.
▸ At the table: The relentless-tomb dungeon crawl. A party explores a buried/derelict site and accidentally wakes something that keeps standing back up no matter how many times they drop it. Slow, inevitable, eerie — fewer enemies that refuse to stay dead. Great for a "we have to escape before it fully reactivates" climax.
Aeldari & Drukhari — the dying elder race
The Aeldari (Eldar) are an arrogant, fading elder species of master psykers and artists — few in number but devastatingly advanced; they meddle in mortal affairs for inscrutable reasons of their own. Their dark cousins the Drukhari are sadistic raiders who survive by stealing the suffering of others. Think proud, alien elves with starships.
▸ At the table: The ambiguous third party. Aeldari make a brilliant frenemy — they show up, manipulate the PCs toward a goal that serves their own ends, then vanish (is the elegant alien helping or using you?). Drukhari are a clean villain: lightning slaver-raiders who strike, grab captives, and flee — a kidnapping/rescue hook.
T'au — the naïve idealists
The youngest race in the galaxy: idealistic, high-tech, communal, expanding under a philosophy called the Greater Good. The closest thing to optimists in this setting — clean battlesuits, energy weapons, actual diplomacy — which in 40k makes them dangerously naïve. The Imperium considers their tolerance itself a heresy.
▸ At the table: The morally-gray opponent that makes players think. The T'au might genuinely offer a better deal than the Imperium — and the grimdark gut-punch is that siding with the "nice aliens" is still treason punishable by death. Use them when you want a fight the players aren't sure they should be having, or a tense negotiation instead of a brawl.
QUICK ANTAGONIST PICKER
Out of prep time? Pick a vibe:
- First-timer-friendly fight → Orks (weak mobs + one big boss) or a Chaos cult (social scene → ritual fight → one elite).
- Horror / tension → Tyranids (ambush in the dark) or Necrons (the thing that won't stay down).
- Investigation / "who's the traitor?" → Chaos cultists hidden among NPCs.
- Moral gray area → T'au (should we even be fighting them?) or Aeldari (whose side are they on?).
- Smash-and-grab plot hook → Drukhari raiders kidnap an NPC; go get them back.
Universal rule: reskin only flavor and damage type — never the underlying 5e math. Fear the swarm, not the boss. A handful of weak mobs plus one clear named villain beats a few high-CR threats every time, and it keeps every round meaningful for new players.