Class and Status
Imperial society is highly stratified between Highborn Citizens, and those of lower statuses.
The Highborn are the result of a system of peerages and hereditary rights granted over thousands of years of Imperial history. The Imperium enshrines and romanticises its Highborn Citizens in its art and media, and attributes many military victories to their number. This ‘nobility’ is wealthy and powerful; some of them resemble ancient nobles directly, while others are more like the Chief Executives of powerful corporations.
The only souls within the Imperium who can claim to command equal respect from all citizens as the Highborn do, are Members of the Ecclesiarchy , the Machine Cult, Imperial Military Officers (who are almost always Highborn anyway) and the posthuman angels of death that are the near-mythological Astartes.
Beneath the Highborn are Lowborn Humans making up the serving, middle and working class of the Imperium and the are most numerous people of the Imperium. Largely dependent on Imperial handouts most Lowborn are poor and uneducated but obedient to Imperial rule - equally the Imperium is terrified of rebellion and subjects them to brutal repression at the slightest sign of it.
Beneath the Lowborn are Abhumans and Mutants. The Imperium is incredibly puritanical about the genetic purity of its citizens, and while artificial augmentation of humans has occurred in its past, deviation from the genetic norm of humankind is considered abominable. To this end, any human judged to be significantly abnormal genetically can find themselves persecuted and relegated to a subhuman status from which there is no escape.