The Imperium of Man, also called simply the Imperium, 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 A.D. It is ruled by the living god who is known as the Emperor of Mankind.
The Imperium of Man is a war-torn stellar empire, teetering on the brink of collapse. For 10,000 Terran years it has been ruled by the deathless Emperor, a being of almost limitless psychic power, to whom thousands of souls are sacrificed daily to provide Him the psychic strength to maintain the Imperium's lines of communication and transport.
The peoples of the Imperium live in a galaxy where Daemons are real, mutation is frequent and death is a constant companion. To be alive in the 41st Millennium is to know that the universe is a terrifying and hostile place. It is a place where you are but one amongst billions and, no matter how heroic your death, you will not be missed.