The Imperium of Man is a galaxy-spanning interstellar Human empire, the ultimate authority for the majority of the Human species in the Milky Way Galaxy in the 41st Millennium. It is ruled by the living god who is known as the Emperor of Mankind.

However, there are other humanoid species classified as Imperial citizens, mainly mutant offshoots of genetic base-line Humans who are known as Abhumans and include such Human sub-races as the Ogryns, Ratlings and Squats.

The Emperor of Mankind is the immortal ruling monarch of the Imperium of Man, and is described by the Imperial Ecclesiarchy and the Imperial Cult as the Father, Guardian and God of humanity. The Chaos Gods and the daemons of the Warp refer to Him as "the Anathema" for He is the greatest embodiment of universal Order in the galaxy today. He has sat immobile, his body slowly crumbling, within the Golden Throne of Terra for over 10,000 standard years. Although once a living man, His shattered, decaying body can no longer support life, and it is kept intact only by the cybernetic mechanisms of the Golden Throne and a potent mind itself sustained by the daily sacrifice of thousands of lives.

Though He is no longer responsive to external stimuli, the Emperor still lies at the very heart of the Imperium's continued existence. Although He cannot be directly involved in the day-to-day running of humanity's galactic government, His existence on the Golden Throne is vital to sustaining the Imperium, since His powerful mind's presence in the Immaterium maintains and directs the Astronomican, the psychic beacon that makes possible faster-than-light Warp travel and is vital to Imperial shipping, transportation, commerce and communication.

The Space Marines, also known as the Adeptus Astartes, are superhuman warrior-monks who fight for the Imperium of Man. They wear mechanised suits of armour and have modified genomes that grant them superhuman strength and endurance. Some Space Marines have betrayed the Imperium and serve the Gods of Chaos, and are thus known as Chaos Space Marines.

They are foremost amongst the defenders of Humanity, the greatest of the Emperor of Mankind's warriors. They are barely Human at all, but superhuman; having been made superior in all respects to a normal man by a harsh regime of genetic modification, psycho-conditioning and rigorous training.

Seven to seven-and-a-half feet tall in their bare feet, Space Marines are untouched by plague or any natural disease and can suffer wounds that would kill a lesser being several times over, and live to fight again. Clad in ancient, eight-foot-tall power armour and wielding the most potent weapons known to man, the Space Marines are terrifying foes and their devotion to the Emperor and the Imperium of Man is unyielding. They are the God-Emperor's Angels of Death, and they know no fear.

The Astartes are physically stronger, far more resilient and often mentally far removed from the lot of most normal Human beings. In the presence of the Astartes, most people feel a combination of awe and fear, and many cultures on the more primitive worlds simply worship them outright as demigods or angels of the God-Emperor made flesh.

They should feel so, for many Space Marines feel little compassion for those they have sometimes termed "mortals" in comparison to themselves, seeing the very people they were created to protect as little more than obstacles to a more efficient eradication of the Imperium's enemies.

The Inquisition, formally called the Holy Orders of the Emperor's Inquisition, is a secret organisation that exists outside of the standard administrative hierarchy of the Imperium of Man. The Inquisition acts as the secret police force of the Imperium, hunting down any and all of the myriad threats to the stability of the God-Emperor's realm, from the corruption caused by the forces of Chaos, Heretics, mutants and rebels, to assaults from vicious alien species like the Tyranids, Orks or Drukhari.

The Inquisition's infamous sigil was derived from the personal heraldry of Malcador the Sigillite, the Regent of Terra during the Great Crusade and the Horus Heresy and the second most powerful psyker in the Imperium of Man after the Emperor of Mankind Himself.

It was Malcador who first created the secret organisation that would later become the varied Ordos of the Inquisition at the start of the Heresy on the orders of the Emperor. The Master of Mankind had ordered the Sigillite to find a group of men and women of an "inquisitive nature" to search out the enemies of the Imperium, whether they lay within or without.

The Inquisition is divided into three major orders or "Ordos Majoris" in High Gothic and many other minor ones, or "Ordos Minoris," each dedicated to confronting a very specific threat to the continued survival of the Imperium and Humanity.

The Inquisitors of the Ordo Malleus and their Chamber Militant, the Space Marines of the Grey Knights, seek to confront and defeat the forces of Chaos and the other threats from beyond wherever they assault Imperial space.

The Ordo Xenos and its Chamber Militant, the Astartes of the Deathwatch, defend the Imperium from the myriad alien threats that lie outside its borders.

The Ordo Hereticus and its Chamber Militant, the pious battle-sisters of the Adepta Sororitas' Orders Militant, seek to combat all of the very Human threats to the Imperium that lie within its organisations or on its worlds.

A Psyker is an individual of any intelligent species in the Warhammer 40,000 universe who possesses some degree of psychic ability or powers. Psychic powers are sometimes referred to as "sorcery" when they are gained or enhanced through interaction and bargaining with the malevolent entities who exist within the Empyrean.

Psykers are also sometimes called "witches" in the Imperium of Man and among the Aeldari, particularly when such powers are used in a way that they show no regard for the dangers they may spawn for others or are used in pursuit of the agenda of the Chaos Gods. All psykers draw their powers from the extradimensional realm known as the Immaterium or the Warp that underlies four-dimensional realspace and is the source of all psychic energy in the universe. As such, psykers, particularly Human psykers whose minds are far less disciplined and easily tempted than their Aeldari counterparts, are often in danger of possession by the daemonic entities of the Warp, insanity and ultimate corruption by the Ruinous Powers of Chaos.

A Rogue Trader is a combination of freelance explorer, conquistador and merchant. They are Imperial servants, given a ship, a crew, a contingent of marines or Guardsmen and carte blanche to roam the worlds beyond Imperial control.

In their task of exploring and exploiting uncharted regions of the galaxy, Rogue Traders might come across worlds harbouring long forgotten human civilisations which will be incorporated into the Imperium. Other times they find empty or alien-dominated planets ripe for colonisation or exploitation.

The Imperial Navy, known as the Navis Imperialis in High Gothic, is one of the primary armed forces of the Imperium of Man.

While the Astra Militarum (Imperial Guard) represents the Imperium's ground forces, the Imperial Navy is responsible for the fleets of starships that maintain order between the stars and planets in the Imperium, for all space and air support provided to the infantry of the Astra Militarum through its Aeronautica Imperialis branch, and for transporting those Guardsmen across the galaxy to the Imperium's myriad warzones.

The battlefleets of the Imperial Navy are constantly engaging threats both inside and outside the Imperium's borders.

In ancient times, during the Great Crusade and Horus Heresy eras, the Imperial Navy was not an independent armed force of its own but was considered a part of the greater Imperial Army and was known as the Armada Imperialis.

Its vessels were dedicated to the defence of Imperial space and strategic Warp routes. This was opposed to the fleets of warships assigned to the service of the Legiones Astartes, who were used for the planetary assaults that occupied the bulk of the Great Crusade.

After the horrors of the Horus Heresy, during the Imperial reformation overseen at the start of the Time of Rebirth by the Primarch Roboute Guilliman, the Imperial Army's fleet component was reestablished as a separate and rival service. This was done to weaken the Imperial armed forces in case of the outbreak of a future rebellion against the Emperor's rule.

The Orks, also called greenskins, are a savage, warlike, green-skinned species of humanoids who possess physiological features of both animals and fungi who are spread all across the Milky Way Galaxy. They are seen by their enemies (pretty much everyone else in the universe) as savage, violent, and crude, but they are the most successful species in the whole galaxy, outnumbering possibly every other intelligent starfaring species, even Humanity (with the very plausible exception of the Tyranids).

Greenskins are one of the most dangerous alien races to plague the galaxy. Numerous beyond belief and driven always to fight and conquer, the Orks threaten every single intelligent species of the galaxy. Orks are possibly the most warlike aliens in the 41st Millennium, and their number is beyond counting. Amid constant, seething tides of battle and bloodshed, burgeoning Ork stellar empires rise and fall. Mercifully most are short-lived, soon destroying themselves in a maelstrom of violence and internecine conflict, but should the Orks ever truly unify, they would crush all opposition.

Orks generate a potent psychic gestalt field that allows them to accomplish many feats of technological engineering that might otherwise seem impossible. At the same time, the power of this psychic field is directly proportional to the number of greenskins present in a given location. The more Orks that gather, the more Orks are drawn to them, at the same time that the power and intelligence of the greenskins begins to grow with their numbers. The Orks' unquenchable thirst for battle has always proved their downfall: historically, the Ork tribes have spent much of their time fighting amongst themselves, waging brutal wars with only the strongest surviving. On occasion, an Ork leader will emerge who is mighty enough to defeat his rivals and unite the warring tribes. His success draws other tribes to him, and soon a great WAAAGH! is underway -- partly a migration, partly a holy war that can exterminate the populations of entire star systems. When the Orks are on the rampage, the galaxy trembles, and in the Age of the Dark Imperium there are more WAAAGH!s rising than ever before recorded.

The T'au (Imperial binomial classification: Tau tau), also spelled Tau in older records and pronounced "TOW," are a young, humanoid and technologically-advanced intelligent species native to the Eastern Fringes of the Milky Way Galaxy.

They are fighting to expand their interstellar empire and extend a philosophical concept they call the "Greater Good" (Tau'va in the T'au Lexicon) to all the intelligent species of the galaxy.

The T'au claim to be a peaceful species when possible, asking if others will join their cause voluntarily instead of fighting against them. However, if their peaceful overtures are refused, the T'au may well decide to conquer a planet and add it to their growing interstellar empire for the Greater Good, searing the flesh from the bones of anyone who stands against their benign intentions.

T'au society is divided into a number of castes, each responsible for managing a specific aspect of their society. The T'au's central motivating ideal is that everyone in their empire regardless of their species of origin will work for the collective betterment of everyone else, an almost mystical philosophy they call the Greater Good.

The T'au are the central figures of the T'au Empire, an interstellar polity which is composed of several different intelligent species, primarily the Kroot of Pech, the Vespids of the world of Vespid and the nomadic Nicassar.

However, there are now several Human T'au Septs derived from conquered Imperial Humans or Humans who voluntarily joined the T'au Empire because they were impressed by the concept of the Greater Good. These people are known as Gue'vesa in the T'au Lexicon and they are considered amongst the most vile of Traitors and Heretics within the Imperium of Man.

The T'au are a relatively young species (it has been only 6,000 Terran years since Imperial Inquisitors first noted that the T'au had only just mastered fire and the wheel), and they have evolved rapidly over the past few millennia. Unlike other young intelligent races of the galaxy, the T'au have made remarkable leaps in technology and now represent a real threat to Imperial domination in their region of the galaxy.

The Asuryani (Aeldarix dolosus) ("Children of Asuryan" in the Aeldari Lexicon), also called Craftworld Aeldari as they were named before the fall of their lost realm, or the Eldar as they were long known to outsiders, are an ancient humanoid alien species whose vast empire once extended the width and breadth of the known galaxy. The Asuryani are a kindred of the Aeldari race who now live on vast, city-like starships called craftworlds.

The Aeldari Empire was without equal, and they counted themselves masters of the stars. But over ten millennia ago, the Aeldari's overweening pride and their fall into hedonistic practices led to a cataclysm that all but eradicated their kind and led to the birth of the Chaos God Slaanesh.

Despite their boundless power, the heart of their civilisation was torn out by this catastrophe of their own making, forcing many of the surviving Aeldari, now calling themselves "Eldar" to outsiders and "Asuryani" among themselves, to flee upon gigantic, continent-size starships once used for commerce and trade that they named craftworlds. Now the Asuryani cling to survival by a thread, fighting the horrors of the galaxy with ritualised mental discipline and consummate martial skill.

The Asuryani rely on mystical technologies like psychocrystalline Spirit Stones and the psychoactive wraithbone Infinity Circuits that comprise the skeletons of their craftworlds to store their souls after death and prevent their consumption by Slaanesh. It is the use of these technologies and their pursuit of a rigid system of behavioural modification to keep their darker impulses in check that shape the Asuryani lifestyle and define their culture as distinct from that of the other Aeldari sub-cultures.

The Aeldari species has a long and complex spacefaring history, so long in fact that little is known for certain about the course of their physical evolution and early planet-bound existence. The original Aeldari homeworld was destroyed during the catastrophic collapse of the Aeldari civilisation known as the Fall of the Aeldari.

The remnants of Aeldari culture that survived the cataclysm among the Asuryani preserved much of their species' history in the form of traditional stories, songs and dance. Written records, monuments and visual records were almost completely destroyed except for a few instances where they were taken aboard voidcraft fleeing from the doomed worlds.

As a humanoid race, Aeldari are physically very similar to Humans, although not entirely identical by any means. They possess longer and cleaner limbs, and fine ascetic features with penetrating and slightly slanted, almond-shaped eyes. Their ears are also slightly pointed, but otherwise they could pass as Human at first glance. The most obvious difference between Humans and Aeldari can only be seen when they move, for the movements of an Aeldari radiate a subtle grace which is impossible for a Human to emulate. This can be seen in even their slightest gestures or the dexterity with which they manipulate small objects.

The Aeldari mind, while similar in general to the Human psyche, is far more inclined towards emotional extremes. Because of this, Aeldari are more intelligent but also far more intense than Humans. Although an Aeldari and a Human can both feel grief or joy, the Aeldari's experience is likely to be far more extreme. This natural inclination towards emotional extremes is both a blessing and a curse to the Aeldari. On the positive side, it gives them an unparalleled appreciation of life and an unrivalled ability to express themselves through music and other creative endeavours. A melody or gesture made with grace and skill can elicit an intensity of pleasure which is unimaginable to a Human.

But this potential for joy is paralleled by an equal capacity to feel despair, ambition and even hatred. Confronted by grief or other personal setbacks, an Aeldari suffers mental torments which far exceed the boundaries of Human anguish. The extreme nature of their temperament makes it very important that the Aeldari maintain a measure of self-control at all times, for it is dangerously easy for them to become entranced by and ultimately dependent upon the experiences that their culture offers them. They must learn to control the darker side of their natures, which is no less an essential portion of the Aeldari psyche -- and the source of the catastrophe that nearly caused their extinction.

For this reason, the Asuryani are defined as a culture by their pursuit of the Asuryani Path. This philosophy teaches them how to balance their potent minds and pursue constructive goals rather than falling to the amoral pursuit of pleasure and selfishness that ultimately destroyed the ancient Aeldari and still defines their dark kin, the Drukhari.

The Aeldari are a naturally psychic species, and all Asuryani possess the potential to become powerful psykers if they choose to pursue this path. The Asuryani can use these innate abilities to shape matter, which lies at the foundation of their extraordinary command of technology.

Though highly advanced and feared across the galaxy, the Craftworld Aeldari are still a dying people in the late 41st Millennium -- a shadow of their former glory -- and their species teeters on the brink of final annihilation.

The Drukhari (Aeldarix malum) (pronounced Druh-KAR-ee) or "Dark Ones" in the Aeldari Lexicon, also known to outsiders as the Dark Eldar, are a forsaken and corrupt Aeldari kindred, the sadistic, malicious counterparts of the Asuryani. Like their cousins of the craftworlds, the Drukhari are an ancient and highly advanced alien race of fey humanoids. The alternative term "Dark Eldar," or Eladrith Ynneas in the Aeldari tongue, was first coined by the Drukhari archon and Supreme Overlord of Commorragh Asdrubael Vect in the 32nd Millennium.

The Drukhari's armies, like their Craftworld Aeldari counterparts, usually have the advantages of mobility and advanced technology, though they are often lacking in resilience and numbers. The Drukhari revel in piracy, enslavement and torture, and are sadistic in the extreme. Drukhari armies make use of various anti-gravity skimmers such as Raiders and Ravagers to launch high speed attacks.

They strike with little or no warning, using an interdimensional labyrinth known as the Webway to traverse the galaxy safely and far more quickly than most advanced starfaring species are able to with their Warp jumps. The Drukhari are unique amongst the intelligent races of the Milky Way Galaxy because they do not live on a settled world or worlds, but rather the bulk of their population is concentrated in one foul city-state -- the Dark City of Commorragh -- that lies within the "ordered" Immaterium of the Aeldari Webway.

The Drukhari are mainly pirates and slavers who prey on targets across the galaxy to feed their unholy appetites for other sentient beings' souls, a terrible desire called "the Thirst," though they are sometimes used as mercenaries by other starfaring species. The Drukhari are the living embodiments of all that is wanton and cruel in the Aeldari character. Highly intelligent and devious to the point of obsession, these piratical people revel in the physical and emotional pain of others, for feeding upon the psychic residue of suffering is the only way they can stave off the slow consumption by the Chaos God Slaanesh of their own souls.

The Drukhari, particularly their warrior castes, are tall, lithe, white-skinned humanoids. Their alabaster skin is death-like in its pallor, for there is no true life-giving sun within their dark realm to provide colour. Their athletic bodies are defined by whipcord muscle, shaped and enhanced until they are physically stronger on average than their Craftworld Aeldari counterparts, as the Drukhari prize physical and martial prowess highly. Yet for all their physical beauty by Human standards, the Drukhari are still repugnant monsters.

When viewed with the witch-sight of a psyker, the Drukhari's black souls are revealed, for they eternally thirst only for the psychic energy of the anguish and torment of other thinking beings in order to fill their own infinite emptiness. Unlike their Craftworld Aeldari cousins, the Drukhari do not integrate their still-powerful latent psychic abilities into their culture, and indeed have a great disdain for psykers of any kind. This is because for the Drukhari, the use of psychic abilities would only further draw the attention of "She Who Thirsts" (Slaanesh) upon them, and their souls are already at risk enough of being devoured by the Prince of Chaos.

The terrifying insectoid monsters that look like they’re tearing their way to eat your face. The Tyranids are an unknowable, immeasurable, apparently unstoppable force of biological annihilation, that came from the depths of space beyond our galaxy, with the express intention of consuming every living thing, everywhere.

Tyranid bio-forms adapt and evolve at great speed, in real time, adopting whatever form necessary to evade, encircle, disable and devour their prey – whether they be a cowering, weeping child, an eight-foot power-armoured Space Marine, or 70,000 acres of coniferous woodland. The ‘Nids are, fundamentally, really not fussed. Encroaching upon us inexorably, planet by planet, in organic armadas known as Hive Fleets, the Tyranid menace is slowly but surely winding its way into every galactic neighbourhood, seeding every world with its self-replicating spores and methodically picking them clean of every living cell, until only a barren husk remains.

These are the metal cyber-mummies with glowing green bits sticking out. They’re the Imperium’s main antagonist in the current era of 40K. The Necrons are the oldest known Xenos race, dating back to before the War in Heaven. Once a large, aristocratic, quasi-feudal empire plagued by the evolutionary straitjacket of a tiny lifespan, the Necrons lived through a tragic series of events that granted its entire civilisation immortality – but imprisoned them in soulless metal bodies.

In despair at the fate they’d wrought themselves, the Necron royalty placed their entire race into stasis in vast underground crypts, awaiting a future time when the galaxy would be ripe for conquest and they could regain their former, necropolitan glory.

And that time is now! Across the galaxy, the numberless metallic hosts of the Necron dynasties are awakening from their long nap, the command protocols of their noble lords gradually booting them up into full-on galaxy-reclaiming mode. On settled worlds everywhere, pyramidic monoliths are rising from the earth, and legions of mind-slaved Necron Warriors emerging to take back what once was theirs.