Emperor of Mankind

Overview
The Emperor of Mankind is the leader of the human Imperium, and is described by the Imperial Ecclesiarchy as the Father, and Guardian. He has sat immobile within the Golden Throne of Terra for over ten thousand years. Although once a living man, his shattered body can no longer support life, and remains intact by a mind itself sustained by the daily sacrifice of thousands. He has sacrificed his immortal life in the service of Man.

To Mankind's countless quadrillions across the galaxy-spanning Imperium, he is nothing less than a god. Through his Imperium, Mankind is held together and forms one of the strongest races in the galaxy, and united, Mankind is able to survive the myriad of threats it faces. The Imperium's rule, carried in the Emperor's behalf by the High Lords of Terra and a multitude of Imperial organizations, has been long and necessarily harsh.

The Emperor is at the very center of the Imperium. Although he is no longer directly involved in its day to day running, his presence on the Golden Throne is vital to sustaining the Imperium, as he originates the Astronomican, making possible faster-than-light warp travel, which is vital to Imperial shipping and communication. He is said to guide his race through the Emperor's Tarot, which select psykers can consult. He is also said to constantly, psychically, battle Chaos and prevent its intrusion upon the material universe. He must be at all times vigilant throughout the entire Imperium.

Origins
Origin 1:

In the current background, the Emperor's origin and history prior to unifying Terra is left mysterious and undetailed. The first mention of the Emperor in Imperial records is when he unified Terra at the end of the Age of Strife. In Horus Rising, Horus mentions that the Emperor lived "in Anatoly, in his own childhood" when talking of his first meeting with the Emperor. It is known he had been immortal and ancient even before his ascension to the Golden Throne over ten thousand years ago, It is also known the Emperor was born in persa and even has been said to have been in most human myths.

The Emperor is the "New Man", the first and greatest of the race of psykers. He is also the collective reincarnation of the extinct Shamans who had guided humanity. As he grew older his powers began to manifest themselves and he gradually remembered his thousands of past lives.

For thousands of years before becoming the Emperor, he guided and watched humanity develop. He was aware that the extremes of human nature were feeding the Chaos gods, and sought to promote peace and harmony, and thus curb the growth of the Chaos Powers. The Chaos Powers themselves recognized the Emperor as their greatest enemy among all the intelligent beings of the galaxy. Only during the Age of Strife did the Emperor emerge to take a more direct hand in the future of humanity, conquering the warring factions and establishing his rule over Earth, accepting the deaths of innocents that would result from his conquest in order to achieve the greater good of unifying humanity and protect it from the predations of the Warp.

With the assistance of the Adeptus Mechanicus on Mars the Emperor created the first Space Marines and fleets of interstellar ships that would carry his armies across galactic space. The objective was a Great Crusade that would unify all planets colonized by man prior to the Age of Strife into one Imperium, and also subdue, destroy, or chase away all alien races from what was to be the Imperial Domain, the manifest destiny of Mankind. The Emperor also created the Primarchs from whom the Space Marines' gene-seed was developed. The Chaos gods, however, sought to thwart his plan. The Primarchs were sucked into the warp, and scattered across the galaxy. During the Great Crusade all but two of the Primarchs were found and united with their Space Marine Legions. As the Emperor traveled across the stars, some wanted to worship him as a god, however he forbade this proclaiming "I am not a god, rather than enslaving humanity I want to free them". However, Lorgar, the Primarch of the Word Bearers Legion, gave into the constant whispers of the Chaos Gods and, after corrupting his legion, sent his first Chaplain Erebus to poison the minds of the other Primarchs as well as their Legions. Just as the Imperium had reached its apex, the Emperor's most trusted son, the Primarch Horus, fell to Chaos and betrayed the Emperor, and along with fully half the Space Marine Legions, started a massive civil war for control of the galaxy. This rebellion is known as the Horus Heresy. Though the Emperor defeated Horus, he was all but destroyed in the battle; only the life-supporting Golden Throne has sustained his living corpse in a kind of stasis, neither dead nor alive.

Origin 2:

The Emperor is the collective reincarnation of all the Shamans. The entities that would became the four Great Powers of Chaos had not yet formed when the Emperor was born. But even before the birth of the Emperor, as humanity grew and progressed, the warp began to become increasingly disturbed, and the Librarians began to lose their ability to reincarnate - instead, upon dying their souls were being consumed by the creatures of the warp. Eventually the Librarians, unable to reincarnate, would become extinct, and without the Librarians to guide them, humanity would fall prey to Chaos. All the Librarians of earth gathered to decide what must be done. In the end they decided to pool their energies by reincarnating in a single body. The thousands of Librarians, as one, took poison, and as one, died. A year later the man who would become the Emperor was born. He would be immortal and so no longer needed to reincarnate. As he grew older his powers began to manifest. Over many millennia, he travelled among mankind, using his ancient wisdom to help where he could.

Rise of the Emperor

The man who would later become known as the Emperor first appears in Imperial records as one of the many warlords struggling for control of Terra during the later part of the Age of Strife. The Emperor undertook a series of campaigns against all the other warlords on the planet that would later become termed as the Unification Wars. During these wars the Emperor employed several military formations - such as the Geno Five-Two Chiliad - that consisted of genetically altered/engineered warriors, who played a significant role in his eventual victory. With this victory, the planet and population of Terra were at last unified under one rule; that of the Emperor. With this achievement behind him, the Emperor then set in motion his plans to take his purpose of uniting and guarding mankind out into the stars, to unify with the bastions of humanity scattered across the galaxy. This undertaking would become known as the Great Crusade.

The Emperor prepared extensively for the Great Crusade; he created the special astro-telepath corps to link his eventual dominion together, and caused the creation of the Astronomican, a supremely powerful psychic signal device powered by the Emperor's own will that would allow simplified and safer travel through the warp. Chief amongst his designs, however, were the creation of superhuman warriors, the logical extension of the gene-troopers already under his command. He had first undertaken the Primarch Project, the creation of twenty infants from his own genetic code, designed to mature into powerful generals for his armies. However, this plan went awry with the intervention of the Chaos Powers. While accounts vary as to exactly what happened, the end of the tale is always the same; the Primarchs were cast into the warp and thought lost. In the aftermath of these events, the Emperor evolved a new plan. Using genetic material which had been derived from the Primarchs, he created a caste of warriors which would possess some of the qualities of the Primarchs. These successors to the genetically-altered warriors of the Unification era were the Legiones Astartes, the Space Marines of the First Founding.

The Emperor led the Space Marines into the reconquest of the Solar System, driving alien enslavers from the moons of Saturn and Jupiter and most importantly, achieving peace and eventual integration with the Mechanicum of Mars. This alliance provided the Emperor with much of the means and materiel to extend his crusade into the stars.

With the final abatement of the warp storms began the Great Crusade. The Emperor's forces rediscovered human worlds, cast out alien oppressors, and claimed new territory aplenty. Perhaps most importantly, the Emperor, leading his crusade, rediscovered his lost sons, the Primarchs. Scattered throughout space, the infants were found one-by-one, over a period of many decades, and reunited with their father and their kin. All were placed in command of the Astartes legions created from their respective gene-seed and played their part in forging their father's Imperium.

First amongst the Primarchs was Horus, first discovered and first honoured. Some great length of time into the Great Crusade, the Emperor decided to return to Terra and placed Horus in charge of the military advancement of his Imperium in his stead. Granting him the title of Warmaster, the Emperor declared that the time had come for his sons to show him what great leaders they were. Turning his back on direct military interventions, the Emperor then created the Council of Terra, the Imperial Tithe, and expanded the civil governing bodies of the Imperium, before retiring in seclusion beneath the Imperial Palace to begin work upon the Golden Throne.

The Horus Heresy

This turn of events did not please all of the Emperor's subjects, several of his sons in particular. In the final stages of the Great Crusade, the Emperor's most trusted son Horus succumbed to Chaos temptation. Horus was told that the reason the Emperor had left the Great Crusade was so the he could attempt to reach godhood, abandon all his sons and betray one of the central tenets of the Great Crusade (to enlighten humanity and free it from the bonds of false gods). Horus saw it as his duty to save the Imperium and turned on his father. Having corrupted fully half of the Space Marine Legions, Horus led them against the Emperor and plunged the fledgling galactic empire into a colossal civil war. This conflict became the most terrible in human history, and billions perished as the Traitor Legions tore apart the empire they had helped to forge.

The last act of this terrible treachery was played out above Terra, as the Emperor led a desperate teleport assault against Horus' flagship. Though the Emperor was a being of unfathomable psychic and physical might, Horus had become mighty indeed, bloated with the powers of all four Chaos gods. After a tragic battle, and though heartbroken at the loss of his favored son, the Emperor finally slew Horus, though the struggle left him close to death. In this state he was found by Rogal Dorn. The dying Emperor dictated plans for the arcane life support machine that would sustain his remaining cells for over ten thousand years, and he was subsequently interred in this altered version of the Golden Throne.

Present Day
The Emperor's broken body was discovered by Rogal Dorn who, following the Emperor's instructions, oversaw the Emperor's connection to the Golden Throne, an arcane device to sustain his mind. The Emperor has remained in the Golden Throne since his 'ascension' to this day, neither fully living nor wholly dead. Although certain disputed material states that this was initially designed as the hub of the Emperor's project to utilize the webway, the Golden Throne also functions as a complex life support device. The Golden Throne itself lies in the Sanctum Imperialis, a great hall in the heart of the Imperial Palace guarded by the Emperor's Companions, a special bodyguard contingent of the Adeptus Custodes. The Emperor's decaying physical form is preserved by the vast machinery of the Golden Throne, which itself is maintained by Techpriests of the Adeptus Mechanicus. His essence is spread out across the whole of the galaxy, watching over as much of humanity as he can manage, in order to keep the Ruinous Powers at bay.

The Golden Throne is also connected to a massive psychic beacon known as the Astronomican, which makes faster than light travel possible by generating a signal by which Navigators are able to navigate through warp space. The Astronomican signal is originated by the Emperor, but is amplified and directed by a choir of ten thousand human psykers. These are selected for their psychic prowess, their ability to control their power, and after having gone through a rigorous process that includes their soul-binding to the Emperor. The life force of these psykers is consumed over the course of several months, which means that replacements must constantly be found and brought to Holy Terra aboard the infamous Black Ships of the Adeptus Astra Telepathica, the Imperial Organization responsible for handling people with psychic mutation. The selected psykers are, for the most part, indoctrinated to accept their fate as their sacred duty, for they are too dangerous to those around them to be allowed to live, and that the sacrifice of their life is the greatest good that they can do in service to the Emperor. Those less willing are sedated and fed to the Throne regardless.

It is said that the Emperor's existence is one of endless pain and suffering, and that it is only his utter devotion to the human race that keeps him from accepting death. Should the Emperor die then the Astronomican will become useless, and humanity will no longer be able to safely travel through the warp (although this may be disputed by the fact that humanity traveled the stars before the Emperor sat upon the Golden Throne, during the Dark Age of Technology and the Great Crusade). The Imperium would become fractured and disintegrate into civil war. The reliance on the Emperor's life force, and the dedication of his subjects to prevent his death is considered to be the basis of the idea of him being the "God-Emperor".

The Star Child
The Star Child background was introduced first in the Realm of Chaos books and mentioned later in the 3rd Edition Warhammer 40,000 guide. The concept is similar to the Eldar potential god "Ynnead" forming in the Infinity Circuit.

The background has two aspects: the first is that the Emperor's soul is currently forming as a new entity (the Star Child) in the warp and that he will be reborn, and the second is that the Emperor had children (Realm of Chaos: The Lost and the Damned).

Over the almost 50,000 years the Emperor walked among mankind he formed many families and fathered children. A few of his descendants have inherited the powers of the Star Child. These are the "Sensei". A hidden group that call themselves the "Illuminati" know the Emperor is failing. They also know of the "Fall of the Eldar" and seek to prevent Man's own fall to Chaos. The Fall of Man to Chaos would create a new Chaos god, and with its birth, a new warp/real space overlap, encompassing the entire Imperium. They gather the Sensei together, protect them from the Inquisition, and pave the way for the rebirth of the Emperor. Their plan is ultimately to sacrifice the Sensei to the Emperor at the moment the Emperor finally fails; he will be renewed, and be reborn as the Sensei-Emperor to again lead his race in person.

While the Star Child background was introduced in the original 40K version, and dismissed as heretical in 3rd edition in favor of the more vague "Iron Men and Stone Men" history, the current Inquisition's "Thorians" believe in a similar concept of the Emperor's rebirth.

The Emperor is the incarnation of the extinct Shamans who, with their prophetic powers and connection to the warp in its natural and uncorrupted form, had guided ancient mankind. After Horus rebelled and destroyed the Emperor's mortal frame, his body and soul could no longer remain as one; his soul melted into the warp, only a tiny core of the Emperor's humanity remaining whole, which was like a small child in a tiny reed boat adrift in the storm of the warp. Since the Emperor's soul survived, there was a possibility that his whole essence could be reborn once more.

In the same way the Shamans died together to reincarnate as the Emperor, the Emperor's death too could herald a new savior. That time would lie far in the future, when mankind's desire for a new savior would strengthen the core of the Emperor's soul and rekindle it to new life.

The soul of the Emperor adrift in the warp is the Star Child. The humans that were left in charge of the Imperium had no real understanding of what had happened to the Emperor. Though the Emperor's body continued to live within the Golden Throne and his mind continued to be a beacon for humanity, his soul is a god waiting to be born.

The Star Child is also suggested as being the compassion which the Emperor thrust from himself in order to destroy his most beloved Primarch-son, Horus. (Inquisition War Trilogy novel series, Ian Watson, Black Library Publishing)

The Inquisition (particularly the Ordo Malleus) has always been at war with the Sensei, the "Emperor's Sons". In 997.M41, Inquisitor Fortez reports that he and his colleagues Alexio and Credo determined the Temple of the Star Child on Levilnor IV consisted of unwitting pawns of Tzeentch, so they eliminated it. It is noted in Rogue Trader that ammunition for the Inquisition's Psycannons and Psyk-out grenades derive their anti-psychic effect from being impregnated with the rare negative psychic energy - the only known source of this energy being the byproducts of the Emperor's metabolism. Realm of Chaos: The Lost and the Damned notes that the Inquisition has discovered this energy can also be produced from rendered-down Sensei.