Lost and damned dating
They are not a single coherent force, but rather a diverse and infinite collection of warbands and hosts under the leadership of Chaos Champions, also known in official Imperial parlance as Renegades and Heretics.
Often Mutants or unskilled cultists may make up the bulk of armies.
These instinctual, formless entities eventually gained rudimentary consciousness and the Chaos Gods were born -- great psychic presences composed of the best dreams and worst nightmares of the galaxy's mortals.
As the sentient races of the galaxy prospered and grew, their hopes and dreams, their rage and conflicts and their loves and hatreds, all fed the growth of the Chaos Gods and nurtured their power.
But there are those few men and women who dedicate their lives to becoming true warriors of the Chaos Gods.
For these devotees, the allure of Chaos is even stronger.
In some cases it is even a mighty Chaos Space Marine who has left his Traitor Legion or Renegade Chapter with his retinue of corrupted Astartes so that he may start his own warband and carve out his own dominion across the galaxy.