A mostly male nobility leads a milita of chattel and peasants. While large portions of the planet are Civilized, outside of those areas is a Catcus Jungle Deathworld (With hidden ancient pyramids, by jove). The nobility lead constant expeditions to raid these ruins.
The miltias tend to be MECHANIZED/HEAVY/INFANTRY that specializes in Close Combat/Shock and Awe tactics. (Bayoneted Rocket Launchers?)
While the coolies are FANATICAL, the nobility themselves are merely Adherents, but tend to disseminate that Mutiny is Heresy in the eyes of The Emperor.
The nobilty also ride Exotic Mounts as status symbols, and often compare their mounts with one another. Typically a form of Krieg horse is common among the nobility, and breeding papers can extend several generations but every once in a while, a particular noble will try to get attention with a mount of another type.
They all fight For the Homeworld. The Nobles in particular compete for Homeworld Status...
Some Nobles get noticed by the Arbites or thee Administratum, and "Old friends" often pull strings for one another.
They are particular enemies of Chaos Space Marines and Chaos Organization Y, while their raiding of old Elder tombs hasn't made them friends of the Dark Elder. Their Sadles also tend to be made of the Finest Sarharduin skins, and imported Sarharduin cavier is a delicacy.