Warhammer 40,000

In the grim darkness of the far future, there is only war!

Warhammer 40,000, also referred to as Warhammer 40k, or sometimes just 40k is a continuum based on the popular tabletop game released by Games Workshop.

The game was originally a rather blatant futuristic expy of the Warhammer series by the same company (as evidenced by most of its races being describable as "X in Space"), but has since grown into its own canon with a dark and gritty feel.

Setting
The game is based on the premise that in the 41st/42nd millennium (hence the 40,000), humanity has spread out across the stars- and promptly come under attack on all sides (including from itself).

Humanity is technically ruled by the God-Emperor of Mankind; however, he is almost dead and only sustained by the great Golden Throne in which he is interred, unable to move or speak. Only his sheer force of will has kept him "alive" for so long. In practice the Imperium is ruled by the Senatorum Imperialis, the twelve High Lords of Terra, and functions as a religious state. To make matters worse, there have been hints that the Emperor's life-support has begun to falter, and when he finally dies, humanity will be doomed, since the Emperor's power is the only thing that makes faster-than-light travel possible.

Most of the Imperium is dystopian- hence the "grim darkness of the far future". The Empire is so massive and sprawling that it includes countless different worlds of all types, ranging from Neolithic jungle death worlds, like Catachan, to polluted hive worlds, like Armageddon.

The Adeptus Mechanicus, the Tech-Priests of Mars, are the engineers and technicians of the Imperium, and create most of the Imperium's more advanced machinery and weaponry, among other things, despite the fact that their understanding of the technology they use is limited at best, with much of their procedure based on ritual and religious dogma rather than genuine engineering or mechanical skill. Actual invention is discouraged, and most new technology created is simply a variation on old technology. The Imperium was originally formed by the re-uniting of the Tech-Adepts of Mars and the Emperor, before his ascension to Godhood. The alliance was dictated by their own religious doctrines in which the Emperor occupies a messianic position of authority.

The Adeptus Mechanicus believe that all knowledge already exists and that humanity only found it. They also see technology as a sort of life form, preaching that the Imperium's machines possess a sort of spirit known as "machine spirit" which only serves humanity. Most ordinary humans don't understand technology at all and assume it is some type of magic.

The Imperium is surrounded by alien species, and is also subject to massive Black Crusades from the forces of Chaos.

The Imperium of Man
The Imperium's defence forces consist of:


 * the Imperial Guard, hundreds of billions of conscripts who hold the line against the Imperium's enemies largely with their bodies alone
 * the Imperial Navy, which navigates the Warp and keeps the connections between the countless worlds relatively safe
 * the Adeptus Astartes, a.k.a. the Space Marines, who are the power-armored special troops of the Imperium. They are implanted with the chapter's gene-seed and through chemical treatment and hypnotherapy they become living weapons platforms that are just barely recognizable as human. There were originally 20 legions of Space Marines. Of these, 2 have no known records. Of the remaining 18, 9 turned to chaos. Some of the remaining legions(and all Space Marines created after these legions) are split into 1000-man Chapters, to limit the possible spread of heresy.
 * the Adeptus Custodes, the Emperor's bodyguard
 * the Adeptus Arbites, the police force of the Imperium
 * the Inquisition, an organisation with almost complete authority dedicated keeping the Imperium clean of chaos and aliens. The Inquisition maintains a force of Inquisitorial Stormtroopers. There are three branches, each with their own specialist force. These are:
 * the Ordo Xenos, which "handles" alien entities like the Tau. They control the Deathwatch, Space Marine veterans chosen for their experience. A Deathwatch Marine knows everything about fighting one enemy, and all about how his chosen weapon works.
 * the Ordo Hereticus, which deals with heresy against the Emperor and the Imperium in general (a surprisingly broad field) Their force is the Adepta Sororitas a.k.a. the Sisters of Battle, female warrior-nuns of the Imperial Cult.
 * the Ordo Malleus, which handles demonic forces like the Warp and the Chaos which has spawned from it. The Grey Knights, an all-psychic force of Space Marines with the best equipment in the Imperium, are the main force of this branch.

The Rest
The enemies of the Imperium include:


 * The renegade forces of Chaos -Crazy mutants and traitors worshiping the Ruinous Powers. Chief among the Chaos gods are: Khorne, the Blood God who revels in death and destruction; Tzeentch, the Changer of Ways who is always plotting something, but his plans are so numerous, complex and self-defeating that only he knows his final goal; Nurgle, the Great Lord of Decay who could be compared to Santa Claus, but with horrifyingly nasty diseases instead of toys; and Slaanesh, the hedonistic and androgynous Prince/Princess of Excess who is pretty much the living embodiment of Squick. Whenever they are not fighting the Imperium or any of the other races, they fight among themselves in an endless battle for supremacy.
 * Eldar -The remnants of an ancient elf-like race which directly created the Chaos God Slaanesh through several millenia's worth of unspeakable acts of debauchery and are now constantly trying to stay one step ahead of him/her/it. Have a complicated relationship with the Imperium in that while the Eldar are Xenos and must be stamped out, they know a lot about Chaos and the galaxy in general, so Imperial Commanders will, on very rare occaisions, join forces with them. Most of the Eldar either live on planet-sized spaceships called Craftworlds.
 * The Dark Eldar -A rogue group of Eldar who constantly commit acts of depravity in order to prevent the Chaos God Slaanesh from eating their souls, namely by taking the souls of those they kill.
 * The Tyranid Hive Fleets - Heavily armoured insect monsters. Devour entire planets, including the atmosphere and the crust. And it's implied that they're fleeing from something even worse.
 * Orks - Big, green, and nasty. The most numerous species in the galaxy by far; the only reason they haven't banded together and easily crushed all opposition is the fact that they tend to spend more time fighting each other. Literally an entire species of biological weapons, as they were created specifically by an ancient race called the Old Ones to fight against the Necrons. They possess a gestalt psychic field called the WAAAGH! that allows most of their technology to work despite it simply not being in working order(guns will fire without firing pins, cars will function with broken engines, and so on). The WAAAGH! is also a time when Orks actually band together to fight other races in a mass migration/holy war/looting party/bar fight that only ends when the WAAAGH! leader is killed or when there's no one else left to fight with. Orks are asexual and reproduce by giving off spores that terraform any viable terrain into specially designed ecosystems capable of "growing" new Orks within months. Entire star systems have been overrun by Orks because of this.
 * The Tau Empire ("Space commies"; blue skinned aliens with very powerful technology, probably the closest thing to "good guys" in the entire setting, and even then that's if you ignore the allegations of forced sterilization, concentration camps, and brainwashing; like the Eldar, they are sometimes allies of the Imperium, and aside from the Damocles and Nimbosa crusades there is usually a truce of sorts between the two empires.)
 * The Necrons -creepy robots which are virtually indestructible and want to subjugate and harvest all life; they used to be an incredibly short-lived race called the Necrontyr, but gave their souls and bodies to the C'tan star gods in exchange for immortality during a war with the Old Ones. They "won", but that came at the expense of becoming mindless slaves to said star gods for all eternity.

To be a man in this continuum is to be one of countless trillions, and probably very dead. Or worse.

In Badfic
In the grim darkness of the future, there is only war. . . and fetish fuel.

The demographics of "people interested in Warhammer 40K" and "people who write fanfiction" don't overlap much, but the canon still has considerable amounts of badfic. Many of these are straight-up porn, using the various super-soldier/alien/transformative aspects of the canon (often quite badly) in the service of the author's personal fetishes. The other most popular form of badfic is your bog-standard god mode sue.

Agents from the Warhammer 40k continuum

 * Agent Rose Marcone (unknown)
 * Agent Mkellin (Imperial Guard; Tanith First-and-Only)
 * Agent Zodfang Gobrunt (Ork)
 * Agent Uriel Thane (Imperial Guard; Praetorian Guard)
 * Agent Alaric Kovalenko (Imperial Guard; Praetorian Guard)
 * Possibly Agent Richi, judging by her use of the Tanith obscenity/blaspheme "Feth", but this isn't known for sure.