Fiction is, indeed, one of the most beloved super-genres of literature, and science fiction is probably the most popular genre. The brave and the bright exploring the utopic golden spires of the future, travelling the immeasurable lengths of the void in search of intelligent life forms both friend and foe alike. Or unveiling the mysteries of lost civilizations older than Earth and far more advanced than ours. Regardless of the story, it is usually a genre you read to flee to a better time, where technology and knowledge helps you to reach what no human of your time can, and to experience adventure and complete amazement for a few moments before returning to the cold and limiting reality.

Warhammer 40K is not the setting for this. It is the setting for you to read and be glad that your world is not like that. To be glad that you do not have the strength of the heroes, or else you would have the same burden. It is a setting of darkness, blood, horror, and utter, complete hopelessness.

But is also a setting of inspiration, by the lengths that individuals whose existence doesn't matter at all in the grand scheme of things are willing to go to protect their ideals, loved ones, or simply their lives. They go beyond all limits - including sanity - to see a glimpse of light from the next sunrise briefly breaking through the dense clouds of ash ridden skies. Just to fight again.

Starting as a tabletop and miniature collecting game called Rogue Trader - Warhammer 40K created in 1987, it was re-released in 1993 titled solely as Warhammer 40K. It was an adaptation of the older, medieval high fantasy themed Warhammer Fantasy (also amazing, but will not be explained here) and eventually suffered big changes to become the current ongoing setting in the second edition. Since then, it came to various forms of media, including videogames, books, comics, a handful of (unimpressive) movies, as well as serving as inspiration to various other media, such as Warcraft and Starcraft.

The setting contains various major races: the brutish and warlike Orks; the dying and stoic Craftworld Eldar, their cruel and pirate cousins, the Dark Eldar; the ancient and relentless Necrons; the springing Utopian (though possibly harboring dark secrets) Tau Empire; the mysterious mutant invaders Tyranids; and the protagonists, the humans, mainly divided in two factions: The Imperium of Man, and the Forces of Chaos.

While the alien races all have significant lore and importance (with the Eldar, Orks and their long gone overlords Old Ones fighting the Necrons in a cataclysmic war eons ago that eventually lead to the creation of the Chaos Gods), the humans have the most significant amount of lore and importance. They created the largest empire in galactic history, empowering the Gods of Chaos with the greatest treason of all, the only thing that permanently halted the complete human domination over all species and started the countdown to total annihilation.

In this setting of black and grey morality, devaluation of human life and bloody carnage, the most important character (besides the all encompassing Chaos Gods) is the God Emperor of Mankind. He is a nameless god-like being (although he himself rejects godhood) born in pre-historic Anatolia. He secretly guided humanity from the shadows until revealing himself in the darkest hour in the 30th millenium, right after human hegemony on the galaxy (a regime known as The Human Federation) was completely broken by the world shattering war against their own robotic soldiers.

The Emperor rebuilt and warred, crafting the Imperium from the efforts of his legions of super soldier Space Marines and the regular forces of the Imperial Army. The genetically enhanced Marines were lead by his powerful sons, the Primarchs but also almost completely destroyed when half of them rebelled against the Emperor, siding with the Chaos gods. By the hands of Horus, his favorite son and arch-traitor, he was placed on the Golden Throne in a comatose state, incapable of doing anything to stop his empire from decaying without his leadership.

The Imperium changed a lot in the 10 thousand years "ruled" by its ascended Emperor, growing to a corrupt theocracy where human lives are nothing else than resources to be spent for the glory of their slowly dying, silent god. Stretched beyond reason, it is in constant war against all the other races in the galaxy, attacked by menaces from within, and every second closer to the catastrophic ending in which mankind (and maybe all life) will finally succumb, and nothing will remain.

And yet, it carries on. By efforts of men, women, and semi gods.

The Imperial Guard, legions of common men and women selflessly throwing themselves at far greater foes, whose courage (inspired by the words of generals and officers, sermons of preachers, and the occasional execution by the grim and iconic commissars), numbers and ingenuity are yet to be calculated.

The Sisters of Battle, fanatic orders of female warriors whose faith in the Immortal Emperor is so grand that it is capable of shattering reality and performing majestic (and fiery) miracles. They fight for the Ecclesiarchy as their only (official) soldiers and the Inquisition as the Witch Hunters, immolating heretics within the borders of the Imperium and, sometimes, beyond.

And the Space Marines, the official army of Warhammer 40K, men uplifted into matchless soldiers by the Emperor's prowess in the fields of mechanics and biology. Hulking masses of muscle clad in the heaviest armor, bearing the largest weapons, fighting the strongest foes. They are as unstoppable in combat as they are in devotion, not to The Emperor (who is not as divine to them as he is to mere men) nor the Imperium, which they themselves built, but to Mankind itself.

And yet, the vast legions of the guard might be broken and wasted by incompetent generals and overwhelming odds. The Sisters of Battle may burn millions of innocents, blinded by their faith. And the Space Marines, rather than guardians of mankind, might bring as much death to humanity as their enemies, uncaring for lives lost to achieve victory. It is the grim darkness of the 40th millennium. There is only war. But as heroes, monsters, or something in between, they will fight until the bitter end, or the very unlikely salvation.

And this is the briefest summary I could compile about Warhammer 40K. A lot of people are at least vaguely familiar with it, and I will be more than happy to answer any question about the lore with the extent of my knowledge and the effort of research.