The Codex Imperialis is a new tome of political wisdom in the course of being written in the early years of the Era Indomitus by the Primarch Roboute Guilliman of the Ultramarines in his capacity as the Lord Commander of the Imperium and Imperial Regent.
Unlike his prior work, the Codex Astartes, completed in the wake of the Horus Heresy ten thousand standard years before as a guide to military tactics and strategy for the Adeptus Astartes, the Codex Imperialis was intended to deal primarily with civilian matters.
The Codex Imperialis was a guide to the reorganisation of the Imperium of Man's political and socioeconomic institutions so as to restore the galaxy-spanning Human realm to a state more in line with the Emperor of Mankind's original ideals of Human betterment during the Great Crusade.
It also was a work of supreme academic scholarship, intended to lay out the first truly accurate history of the Imperium from the time of the Great Crusade to the beginning of the Era Indomitus with the birth of the Great Rift, unencumbered by propaganda and religious superstition in line with the original ideals of the Imperial Truth long-forgotten by the present-day Imperium.
- Dark Imperium (Novel) by Guy Haley, Ch. 10