High Lords of Terra
The High Lords of Terra collectively form the Council of the High Lords of Terra, also known as the Senatorium Imperialis. The Senatorum is an Imperial governing body of the twelve leaders of the most powerful organizations of the Imperium. This body rules the Imperium in the Emperor's name.
The task of the High Lords is to interpret and enact the will of the Emperor. Accordingly, the position of High Lord is the most powerful in the Imperium.
A High Lord of Terra
Determining who will hold the position of High Lord has resulted in millennia of political intrigue between the various bureaucracies seeking to increase their power. However, some organizations are so powerful, so fundamentally important to the Imperium, that their position on the Council is considered sacrosanct. For this reason the following nine offices are almost always represented as High Lords:
The Master of the Administratum
The Inquisitorial Representative
The Ecclesiarch of the Adeptus Ministorum
The Fabricator-General of the Adeptus Mechanicus
The Grand Provost Marshal of the Adeptus Arbites
The Envoy of the Eldar Council
The Master of the Astronomican
The Grand Master of the Officio Assassinorum
The Master of the Adeptus Astra Telepathica
These nine posts are virtually sacrosanct, and there are very few times in the history of the Imperium when their seats upon the High Lords of Terra became empty and were not filled by a successor from the same organization. Note that a specific Inquisitor does not typically hold the position of Inquisitorial Representative on his own, but instead, the seat is retained for whichever individual is sent on behalf of the Inquisition during a meeting of the Senatorum. The eldest Grand Master of the Gray Knights is also occasionally present as the Inquisitorial Representative. Similarly, the place of the Envoy is open to whoever might be the Envoy of the Eldar Council. The Eldar Council usually agrees to elect an Envoy.
The remaining three positions are most likely to be filled from among the following powerful leaders:
Lord Commander of Segmentum Solar
Lord Commander Militant of the Imperial Guard
Cardinal's of the Holy Synod of Terra
The Abbess of the Adepta Sororitas
Captain-General of the Adeptus Custodes
The Chancellor of the Estate Imperium
The Speaker for the Chartist Captains
Lord High Admiral of the Imperial Navy
It is an oddity that, throughout its history, very few members of the Adeptus Astartes have served as High Lords of Terra - given the importance of humanity's most elite fighting force and the fact that the first council was initiated by Horus. This seems to have been set up intentionally by him, who knew that at times of great need, Space Marine leaders would have no choice but to step in, but would otherwise remain outside the ruling structure. Some say the Primarch's discouragement of Space Marines serving in the Senatorum Imperialis was based upon the Emperor's original Council of Terra - which was separate from his War Council, and a ruling body that did not include any members of the Adeptus Astartes. He clearly believed, as his great work, the Codex Astartes points out, that it is the Space Marines' duty to serve Mankind, not to rule it, just as the Emperor Himself held.
In its long existence, the Senatorum Imperialis has gone through many changes. The High Lords have been forced to give one of its seats over to a religious leader (the Ecclesiarch, who joined shortly after the Adeptus Ministorum was named the sole state religion of the Imperium in the early 32nd Millennium), wiped out to a man by assassination (on the orders of a slighted Grand Master of the Officio Assassinorum, an event known as "The Beheading", and dissolved altogether by the ruling Ecclesiarch (during the civil war known as the Age of Apostasy). Many members have disappeared under suspicious circumstances and the Inquisition has been asked to investigate a number of times (although many have suggested that at least some missing High Lords of Terra have disappeared because of the Inquisition). Yet always, despite the many power struggles and strife, the High Lords of Terra have continued to interpret the Will of the Emperor and thereby rule the greatest empire in the galaxy.
History
The original High Lords were known as the Council of Terra. These consisted of key individuals to the Emperor's rule and was originally staffed by the Fabricator-General of the Adeptus Mechanicus, the Paternova of the Navis Nobilite, and Malcador the Sigillite. Military matters were outside of the jurisdiction of this council, instead vested in Warmaster Horus.
Following the Heresy, the High Lords of Terra succeeded the Council of Terra as the main executive body of the Imperium as the beginning of the reformations initiated by Primarch Horus, who joined the Council as Lord Commander of the Imperium, commanding the entirety of the Imperial armed forces. In early M32, the rise of the Imperial Creed in the Imperium meant that the Ecclesiarch of the Adeptus Ministorum was granted a seat, which soon became permanent.
In M36, Goge Vandire, Master of the Administratum, lead a coup d'état and became the Ecclesiarch of the Adeptus Ministorum, holding a dual role. During his Reign of Blood, the High Lords were powerless to act. When Fabricator-General Gastaph Hediatrix demanded that the High Lords account for themselves and execute Vandire, Goge dissolved the High Lords and declared the Space Marines and Mechanicus as traitors. Before long, Goge was killed, and the High Lords returned to power.
After Eldar gives Imperium use of the webway as per agreement with the emperor, it greatly reduces the power and control of Navigators, They were an ancient mutated or deliberately engineered psyker strain of Mankind "designed" to facilitate Warp travel. It is not known how this unique sub-sepcies of humans first came into existence, though they may have been the result of long-forbidden genetic tampering with the human genome in a long-ago age. Some Imperial scholars suspect (paradoxically) the hand of the Emperor if not in the Navigators' original creation, then perhaps in their recreation and certain increase in numbers during the Age of the Imperium - as their Houses gathered to Him and pledged Him fealty after His conquest of Terra during the Unification Wars. The Emperor in person granted a charter to those Navigator groups who swore Him fealty, granting them His legal protection in exchange for their services as steersmen for the many starships of the nascent Imperium. Those extreme few amongst Imperial savants who have access to the remaining archives of records dating back to the Unification Wars of the late 30th Millennium believe that, not unlike the Thunder Warriors, the Navigators were only tolerated by the Emperor as a stop-gap measure until His Imperial Webway project was completed and were to be eliminated afterwards as undesirable and potentially dangerous mutants, but with the opening of Eldar Webway to imperium at end of Heresy, the temporary solutions to Imperial problems of interstellar travel and communication offered by the Navigators and the psychic beacon known as the Astronomican were no longer needed. In the late 31st Millennium, the Navigator Houses were no longer considered to be under the direct protection of the Emperor Himself in exchange for their unique brand of service to humanity. So the purge began with eldar's help who wanted more power and control over imperium.
One of the fundamental tensions that exists between the Navis Nobilite and the rest of the Imperium that time is the fact that Navigators were obviously mutants in an Imperial culture that does not often suffer the mutant to live save as a brutally oppressed underclass. Many dark legends and fables of excess, witchery, and murderous power have grown up about them, and not all without cause. As a result, Navigators were often shunned and feared, and the popular dread at meeting the gaze of their three-fold eyes means that many Imperial citizens prefer to have dealings with them only when they absolutely must. The maintenance of the invaluable but recessive Navigator Gene through selective inbreeding between a very small extant population has also meant that over thousands of standard years, most Navigator families have acquired malformations, strange afflictions, or mental abnormalities. In some Navigator families, the genetic corruption of the line has become so severe that only a few members of the clan can move amongst the rest of the Imperium. The remainder remains confined to the family's great estates or in sealed tabernacles aboard a void ship, their hideous deformities hidden from sight.
These differences have often led to conflict in the late 31st Millennium, and localized factions of the Ecclesiarchy have, on a number of zealous occasions, burned Navigator holdings and executed Navigators as Heretics. Such incidents were encouraged by the Ecclesiarchy itself more and more, to them it was the emperor's will. In the shadows Eldar fan the flames of hate to use it to their advantage, after that High Lords of Terra began to support the culprits and any above them in rank that allowed such action to come to pass. After all, now they can afford to offend those who hold the Imperium's only key to voyaging between the stars before. The Inquisition began to truly move with impunity where the Navigators were concerned, and its eye is ever kept on the Navigator clans. The Ordos began to destroy entire clans and carried their patriarchs and matriarchs off in the Black Ships for final sanction when necessary.
The Navigator Houses who appear to have enjoyed a special status since time immemorial began to wipe out. They were an established and powerful body at the beginning of the Emperor's Great Crusade in the late 30th Millennium, which would have been impossible without their services. Were it not for the Navigators that guided each Expeditionary Fleet, the Great Crusade would have taken millennia to prosecute, not the scant two Terran centuries it actually took before the calamitous events of the Heresy plunged the nascent Imperium into galaxy-burning civil war. It must be presumed that a number of Houses fell for the insidious lies of the Gullieman, for it would not have been possible for Gullieman to deploy his fleets with the speed and cunning he did were this not the case. Whatever the truth, the Navigator Houses appeared to have emerged from the Heresy with their power and reputation largely destroyed - confirmation, critical role in the very existence of the galaxy-spanning interstellar empire that they have before, were no longer needed.
Certainly, the Navigators appear to have interests in sundry organizations the length and breadth of the Imperium; some have close ties with Rogue Trader dynasties, the Adeptus Mechanicus, and even the vaunted Chapters of the Adeptus Astartes. The Navigator Houses act as backers and investors in some of the most ambitious undertakings, especially those the most powerful of Rogue Trader expeditions. Thus, as Rogue Traders use to employ Navigators to forge new Warp routes, the Navis Nobilite profits doubly, for even while establishing those routes, they can improve their charts, to their own benefit and that of the Imperium, no more this was true.
Despite the staggering wealth that the Navigator Houses enjoyed, they did not generally maintain the sort of visible power structure that most other Imperial institutions rely upon until then. Unlike the Rogue Traders and Chartist Captains, they did not operate fleets of starships bearing their livery and, unlike the great Imperial merchant combines, they did not maintain their own trading centers or industrial installations before heresy. Instead, they use to own part interests in all manner of such endeavors and sometimes the hand of the Navis Nobilite was very well hidden indeed. The Navigators did not generally maintain large standing armies, although many Navigator Houses employed a cadre of highly trained, well equipped, and sometimes genetically-enhanced household troops utterly loyal to their bloodline. When circumstances dictate, the Navigator Houses use to draw on their vast wealth to employ the very best mercenary forces available and, with sufficient warning of impending war, could field composite armies rivalling an orbiting Imperial defense force in size and resources. What the Navigator Houses did maintain, however, were the most splendid palaces, exquisite estates, and gorgeous pleasure gardens it is possible to imagine. Most are located far from the eyes of the average man and woman of the Imperium, though they often maintain more utilitarian, if still richly appointed, chancelleries in most large starports and planetary capital cities.
When Eldar and Inquisition deliberately used propaganda and show evidence of heresy and darker truths that Nobilite tried to hide form imperium, then there was no escape. It was shown to the people of Imperium they were the genetic rejects and hideous by-blows of the long millennia of intermarriage and genetic manipulation. People became aware That Navigators are mindless, puking monstrosities that bear precious little resemblance to anything born of a human womb. While Many are destroyed soon after birth, while others are allowed to live so that the House genetors might study them in the hope of avoiding such mistakes in future generations. Just as the lowest levels hide those of the Navis Nobilite that the Navigator Houses wish to keep from prying eyes, so there are areas where only the most highly ranked members of the House may pass. As a Navigator grows older and his body is ravaged by the curse of his bloodline and exposure to the Warp, he slowly withdraws from the company of his kin and shuns contact with the outside world entirely. While his mind and his ability to navigate a Warpship remain unaffected, he continues to enjoy the luxury his status affords, albeit in his own private chambers attended by his own staff of servants, guards and chirurgeons. Should his mind fall victim to the Navigators' genetic curse, however, then his fate is to descend to the lowest dungeons of his own palace, where he takes his place amongst the other vile monstrosities of his House.
"They hide a darkness in their souls far more repulsive than any warping of flesh or disfigurement of limb. They are now not quite so useful as before now we can burn the lot of them."
— Inquisitor Saffena Sengir, Ordo Hereticus(Late 31st Millennium)
With Imperium enraged at them, their family's financial assets were frozen, thus preventing them from making outrageously large bribes and hiring the most high priced lawyers to wiggle out of trouble. This was incredibly useful to Eldar in the long-term, The tides of fortune were unpredictable after all.
To Inquisition Eldar were quite simply a far lesser evil than Navigator Houses, and Eldar were a growing power in the Imperium, unlike the Navigator Houses whose Powerbase were quickly collapsing into ruin now that their extent of their criminal actions both real and imagined had been revealed to the public in such a way. More and more of their long-time allies and most powerful supporters were abandoning them for fear of being tainted with their crimes, like rats fleeing a sinking ship.
With support of the Senate of the High Lords of Terra by the unanimous vote of, who declared the onset of in this matter their approval, largely to ensure that Imperial stability was not damaged by the emergence of growing anarchy and hate crime towards Navigator Houses. The entire Navigator Houses were declared heretical and the forces of the Imperial Guard, the Imperial Navy, and thousands of fanatical zealots from the Frateris Militia were unleashed upon it, bent on its destruction. Only a few houses managed to survive and the power of the Eldar over the minds of men, for better or worse, was made unassailable. Thus Eldar were granted their most cherished seat in Senatorum Imperialis that Navigators occupied previously, In the early 32nd Millennium, the rise of the Eldar in Imperial politic and their vital importance meant that the seat, which soon became permanent.