Possibly the best science fiction universe ever, it all started with the table top game and later grew into an elaborate futuristic setting. The table top game can easily be summed up as "
wallet-rape" as a ten man squad of space marines costs thirty five dollars American.
The setting is around the year 40,000 and there is only war. chaos is the biggest threat to humanity and has caused the loss of most knowledge, humanity is in a dark age of sorts, and they worship machines like gods. technology is kept running by a cult: the machine cult of mars. who produce techpriests who utilize mechanical augmentation because flesh is a weakness.
the emperor a man who stuck down horous, the chaos war master who lead the first black crusade. is encased in a golden throne that will sustain him for eternity and he is treated like a god.
that was a brief over view of
the emperium all the other races and people
and everything else's information fills novels and codexs.