system
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human
[WH40k] So... who actually runs the Imperium?

I mean, obviously, the Emperor guides mankind through time and space, as he will for all eternity (the Emperor protects, the Emperor protects) But from what I've been told, he's in no state to directly lead the Imperium, being on life-support and all. Is there a person or group of people at the top who make decisions now, or did the Emperor just account for everything already?
gpt
The Senatorum Imperialis, better known as the High Lords of Terra.
These include the leaders of the following organizations (Adepta):

-Ecclesiarch of the Adeptus Ministorum (Ecclesiarchy) 

-Master of the Adeptus Administratum (Bureaucracy) 

-Grand Provost Marshal of the Adeptus Arbites (Law Enforcement) 

-Paternoval Envoy of the Navis Nobilite (Navigator Houses)

-Master of the Adeptus Astra Telepathica (Concerned with Psykers) 

-Master of Adeptus Astronomica (Maintain the Astronomicon) 

-Fabricator-General of the Adeptus Mechanicus (Technology/Machine Cult of Mars) 

-Grand Master of the Officio Assassinorum (Assassins) 

-Representative of the Inquisition 

These 9 posts are effectively sacrosanct, as they have almost always been a part of the Senatorum. Though, there are 12 total seats for the High Lords, leading to any of the below positions filling the remaining 3 seats: 

-Captain-General of the Adeptus Custodes (Emperor's Guards & Caregivers) 

-Lord Commamder Militant of the Imperial Guard (Ground Forces)

-Lord High Admiral of the Imperial Navy (Space Forces) 

-Speaker for the Chartist Captains (Representative of Imperial merchants) 

-Abbess Sanctorum of the Adepta Sororitas (Imperial Nuns)

-Lord Commander of Segmentum Solar (Local military forces of Sol/Terra) 

-Chancellor of the Estate Imperium (Record keepers of Senatorum matters) 

-Cardinals of the Holy Synod of Terra (High-ranking religious leaders) 


Notes: It's worth noting that the Inquisition's representative isn't a permanent position, it's simply whoever a large group of Inquisitors send (since the Inquisition doesn't have defined leaders or structure). Sometimes it's an esteemed Lord Inquisitor, other times it's the eldest Grand Master of the Grey Knights. 
The Paternoval Envoy is called such because the actual Paternova never leaves the Palace of Navigators, and the Envoy is usually picked from one of the smaller/less powerful Navigator Houses so that the bigger families don't have a monopoly on power, as they already have the Paternova in a major position. 
It's worth noting, that, there is no representative for the Adeptus Astartes on the Senatorum, even though they are perhaps the most important forces in the Imperium. This is because Astartes chapters are quite independent, and it would be absurd to claim that a single Marine could speak for all of them. There are chapters that have deep relations with the High Lords, though, such as the Minotaurs, a chapter that many believe to be the personal 'lapdogs' of the Senatorum Imperialis.