High Lords of Terra

The High Lords of Terra collectively form the Council of the High Lords of Terra, also known as the Senatorum Imperialis. The Senatorum is an Imperial governing body of twelve leaders of the most powerful organizations of the Imperium of Man. 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 politically powerful in the Imperium. Since the Emperor can no longer govern his empire directly, it is the claim of the High Lords that his immortal will is known to them and the Emperor rules through the High Lords of Terra. Though the Imperium is too vast to be centrally governed, the High Lords ultimately make decisions affecting the lives of trillions.

History
Following the Horus 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 Roboute Guilliman, who joined the Council as Lord Commander of the Imperium, commanding the entirety of the Imperial armed forces. In the early 32nd Millennium, the rise of the Imperial Creed and the Cult of the Saviour Emperor to become the state religion of the Imperium meant that the Ecclesiarch of the Adeptus Ministorum was granted a seat, which soon became permanent. In the 36th Millennium, High Lord Goge Vandire, Master of the Administratum, lead a coup d’état and became the Ecclesiarch of the Adeptus Ministorum, holding a dual role over the two most powerful organizations of the Imperium. During his Reign of Blood, the High Lords were powerless to act. When Fabricator-General Gastaph Hediatrix demanded that the High Lords finally account for themselves and execute Vandire, Goge dissolved the High Lords and declared the Space Marines and Adeptus Mechanicus to be traitors to the Imperium. Before long, Goge was killed, and the High Lords returned to power, though major reformations followed to prevent any one man from ever again seeking to replace the Emperor as the true ruler of mankind.

The High Lords
Although the sources regarding the exact composition of the Senatorum Imperialis are varied, some institutions and organizations within the Imperium are so powerful that their leaders can be considered a de facto High Lord. The following nine offices are almost always represented as High Lords: The total number of High Lords is said to be twelve, leaving three non-permanent openings. These positions are most often filled from among the following powerful Imperial leaders:
 * 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 Paternoval Envoy of the Navigators
 * The Master of the Astronomican
 * The Grand Master of the Officio Assassinorum
 * The Master of the Adeptus Astra Telepathica
 * Lord Commander of the Segmentum Solar
 * Lord Commander Militant of the Imperial Guard
 * Cardinal(s) of the Holy Synod of Terra
 * The Abbess Sanctorum of the Adepta Sororitas
 * Captain-General of the Adeptus Custodes
 * Chancellor of the Estate Imperium
 * The Speaker for the Chartist Captains (representative of the Imperium's merchants)

The position of Inquisitorial representative to the Senatorum Imperialis is not held by any specific Inquisitor, but the seat is retained for whichever individual is sent on behalf of the Inquisition. The eldest Grand Master of the Grey Knights is also occasionally present as the Inquisitorial representative. Similarly, the place of the Paternoval Envoy is open to whoever might be the Envoy of the Paternova (the elder) of the current ruling family of Navigators. To prevent a monopoly on power, the strongest Navigator houses usually agree to elect a Paternova from the weakest Navigator houses. If a strong house were to rise to power in the Council, that house would gain control of the Navigator's voice in the Imperium and thereby control all but the strongest Navigator families.