High Lords of Terra

Four of the High Lords of Terra. From left to right: the Inquisitorial Representative, the Lord Commander Militant of the Imperial Guard, the Master of the Administratum and the Fabricator-General of Mars. Not pictured: common sense or the Grand Master of Officio Assassinorum hanging over their heads.

"Functionaries are like books in a library: the higher they are, the least they serve."

– Georges Clemenceau

"The measure of a man is what he does with power."

– Plato

The High Lords of Terra (aka “Asthmatic Assholes”) are the twelve members of the Senatorum Imperialis, the Council of the High Lords of Terra, and the rulers of the Imperium of Man in the Emperor's absence.

Overview

After Horus got his heresy on, the Emperor had to "ascend" the Golden Throne to keep himself alive. Since he wasn't dead, Roboute Guilliman reasoned that a new leadership was needed to guide the Imperium. He took the job of Lord Commander of the Imperium from Rogal Dorn and set up the High Lords from the old Council of Terra, inviting the heads of the Administratum, the Officio Assassinorum and the Adeptus Mechanicus to the table as well. As time went on, the Ecclesiarchy, the Inquisition, the Navigators and others were also invited. They seem to have influence over the Minotaurs.

While it's plainly evident that they are not making the Imperium better, there is some evidence that they may be making the Imperium worse than it actually needs to be (although whether this is due to malice or incompetence is anyone's guess, most people are betting on the latter). Exactly what they decide on isn't clear either. "Making decisions that affect the whole galaxy" sounds like a lofty purpose but really all the different departments seem to do things by themselves. The Space Marine chapters decide where they fight, the Inquisition governs itself, the Navigators govern themselves, the Administratum is like a machine just left running and doesn't even change gears... so unless they are just the people with the stamps to approve everything, we need some more fluff on what they are doing GW!

Well good news, I guess: as of 6th they are becoming more and more pro-active. AND in the new series The Beast Arises has them as the main characters and thus we can finally see how they run things. TL:DR oh, my God-Emperor, they're worse than the fans believed. During the War of The Beast, about half the High Lords were politicking and trying to use the biggest Ork WAAAGH! in their favour, getting billions killed along with dozens of Space Marine Chapters and even, it seems, a Primarch. The others tried to deny its existence entirely, leaving only the Grand Master of Assassins to deal with reality (go figure why he wanted to kill the jackasses). Funny enough they're also all portrayed as being very good at their jobs (the Imperial Navy High Lord is a skilled admiral, for example), they're just too focused on the interests of their own factions to work together. Of course, then the Grand Master of Assassins did The Beheading.

For the times the present day 41st millennium High Lords are mentioned, they tend to be treated with rather neutral tones. Typically the fluff only brings up their reactionary declarations to military matters and nothing about their politics, leaving their effectiveness and competence open to speculation. Given that Warhammer 40k is often about Your Dudes ("Your Setting" in this case), this is likely intentional.

The High Lords at the end of the 41st Millenium and the Rise of the Primarch

Watchers of the Throne: The Emperor's Legion has actually finally given us details about the High Lords during the Fall of Cadia, giving us a full list of names and allowing some to show political opinions (Mostly concerning the proposed usage of the Adeptus Custodes that is the main issue for the first half of the book), but considering that Guilliman replaced many of them and the book states that members tend to have short reigns due to the stress of the job resulting in early deaths and/or retirement, who knows what they are like now, if any are still around. Lev Tieron, the Chancellor of the Imperial Council of the time, notes that many of the High Lords he'd known and read about were technically mad, obsessed, or just plain power-hungry, but that they were still the best qualified to do their jobs. Make of that what you will by comparison. Indeed, Tieron's successor Anna-Murza Jek (who currently holds the post) would be assisted by a retired Tieron in defeating the Hexarchy coup after she became suspicious of their actions.

Vaults of Terra reveals another far darker side to the High lords. At least 3 of them were involved in a massive conspiracy to smuggle / lure (potentially a bit of both) a Dark Eldar Haemonculus onto Terra and into the Palace so that he could fix the Golden Throne / try to resurrect the Emperor. Insanity of the plan aside, it goes without saying that the High Lords had also given considerable "payment" to the Dark Eldar in exchange (read LOTS OF slaves and torture victims). They even contrived to attack various parts of the Inquisition in order to keep the secret. This worked surprisingly well, right up until the conspirators tried pulling the same trick with the Custodes who promptly carved them to pieces. Even whilst the Great Rift was unfolding, the conspirators still tried to keep covering their bases, ignoring the Astronomicon failing in order to cover up their dirty laundry. Far less doddering incompetence and far more sneaky bastarding evil.

An important part of Terra's political background is the so called "Static" tendency, namely the belief that the Emperor, via the Council of Terra had come up with pretty much the best way of running the Imperium and that any deviation from that was only slightly better than outright heresy.

As of the Gathering Storm, Roboute Guilliman came back to Terra and proceeded to go full 'Powerfisting-mode' at several members of the High Lords following an attempted civil coup d'etat against him, replacing them with people Papa Smurf (seemingly - see below) trusted in the capabilities and competences of. The other High Lords who were not removed were given a mean look by the Blue Wonder and were essentially given a second chance with Robby keeping a close eye on them. Regardless of affiliation, the Council was rocked by the change to thousands of years of them on top, as well as the colossal waves of reforms put in place by Bobby G.

This lasted about as long as it took for Guilliman to head off on the Indomitus Crusade, wherein several High Lords (and two prior incumbent deposed by Guilliman) attempted to stage a coup against Guilliman in absentia, to the extent of indirectly allowing chaotic cults to flourish on Terra, thereby granting themselves the forces and powers necessary to take over, including the entire Minotaur's Chapter. The Custodes, Sisters of Silence and Assassins promptly intervened immediately after the couple of hours it took for the Custodians to notice, the traitor high lords were permanently ventilated, the Minotaurs forced to obey by the replacament Mistress of the Administratum, and replacement Lords drafted in. It's implied that Guilliman predicted that something like this would happen, so at least he's aware of what the council is like. It also adds an interesting possibility that Guilliman deliberately stacked the council with potential liabilities/left them in (he could have flooded the first redraft with reformers, but didn't) so that he could later replace them with the competent loyalists after those tendencies were proven suspect got themselves killed along with the Cults they had let form, purging Terra of traitors of both Chaos and power hungry moron kinds in a matter of hours.

Members

The High Lords are theoretically a dynamic body of 12 (or 13; see below) members that changes based on the needs of the Imperium. That this is the same number of members as are on the Skaven council of 13 is something we're probably not suppose to notice. The Senatorum Imperialis is bigger and includes the High 12/13, but these are the guys that actually matter, plus a few more with similarly but not-quite as important roles being given descriptions.

Nine Permanent Members

In reality, the same nine old fucks decide everything millennium in and millennium out because they/who they represent are just so influential, leaving only 3 seats up for grabs. These nine guys are:

• Ecclesiarch: The Space Pope, the leader of the Adeptus Ministorum, or Ecclesiarchy. Was granted a seat in M32 for the first time, seat which became permanent three centuries later. During the Age of Apostasy, the Ecclesiarch briefly usurped the Master of the Administratum as most powerful High Lord. Goge Vandire solved that problem by being head of both, then went nuts with power and had to be killed by the proto-Sisters of Battle after Custodes informing them of the Emperor's will that Vandire must die (incidentally allowing the Sisters to prove their loyalty and to be accepted as the official Ecclesiarchy armed force through the pre-arranged exact wording of "no men under arms" in the reform laws by Vandire's replacement Ecclesiarch Sebastian Thor and the other High Lords at the time). As of M41/M42, the Ecclesiarch is considered tied with the Fabricator-General and the Grand Master of Assassins for third most powerful High Lord. Baldo Slyst was fired by Guilliman from this post, and joined in Irthu Haemotalion's failed Hexarchy coup and was shot by a Vindicare Assassin. Baldo's replacement Eos Ritira is the current Ecclesiarch and he is seen as a reformist.
• Fabricator-General of Mars: The head of the Adeptus Mechanicus will occasionally take time from meditating on the Omnissiah or running his/her own nation to help run the Imperium. The only member of the 'High Twelve' that isn't regularly stationed in the Palace itself, mostly due to practical reasons: the most recent one had great difficulty attending meetings in the 'flesh' owing to being augmented to the size of a small building. Luckily, Mars is close enough to Terra to allow for old-fashioned vox communication so it is in the end but a minor hassle. He also seems to have an unspoken role of being the one to lead repairs and maintenance of the Golden Throne.
• Grand Provost Marshal: Head of the Adeptus Arbites. Makes sure the Imperium's myriad jackboots know whose skulls to bust. Often the head of the Arbites on Terra, which is actually a pretty good qualification, as Terra is one mean beat. Aveliza Drachmar was the previous Grand Provost Marshal, taking part in the coup as one of the plotters who wasn't fired from their job earlier but was upset by the Custodes being sent on missions away from Terra, citing Lawful Stupid reasons. Got shot by a Vindicare Assassin on orders of Fadix.
• Inquisitorial Representative: A member of the Inquisition, sent to insure that the Emperor's pet psychopaths are up to date on what laws to enforce, which can be difficult given how factionalized the Inquisition has been shown to be in fluff. An Inquisitor's term is 5 years after which he has to step down to make place for another. It is interesting to note that while there is hefty political competition for the other seats, the seat of Inquisitorial Representative carries little merit because it prevents an Inquisitor from carrying out his primary duty: to directly protect the Imperium from its many enemies by working in the field, not from working at one of the shiniest of desks in the galaxy. They are selected, often unanimously, from Inquisitor Lords from the sectors near Terra, granting the individual the title of Inquisitor Lord Terra even after his service ends. On the plus side, the Inquisition mostly runs on an "influence" system, and becoming the Inquisitorial representative gives the Lord Inquisitor in question a substantial boost in influence. Furthermore, one almost never becomes a full-fledged Inquisitor (let alone a Lord Inquisitor) without a lot of hard-earned field experience doing dirty work in the nastier parts of the galaxy, so the Inquisitorial Representative is likely to be one of the more competent and practical members of the bunch (whether the Inquisitor in question is entirely sane and rational is another matter altogether). However, in rare cases the Inquisition is too busy to send a representative because Xenos and Chaos incursions are too numerous. It's been noted by Imperial historians that whenever there wasn't a representative from the Inquisition on the High Lords to keep things in check, bad things happened.
• Grand Master of Assassins: Perhaps equally surprisingly, the other High Lord who often acts as a check and balance for sanity (for reasons which, if not obvious, will will become apparent if you read The Beast Arises series) is the head of the Officio Assassinorum, and an informal watchdog of the Council. The Grand Master is constantly watched by the other High Lords, out of concern that he might assassinate the others - mostly because one Grand Master did. Funny story. It's seen as tradition for the Master of Assassins to send back the corpses of the other High Lord's spies periodically, as a polite reminder that they do not tolerate the other lords messing with their business. His situation in the council is a bit complicated: theoretically, the Officio Assassinorum is a branch of the Administratum, so this guy has the Master of the Administratum as his boss. Also, he needs the whole council's approval to send out his assassins away from Terra after a target as per Big.E's edict. On the other hand, any attempt by the Master of the Administratum (or any other High Lord) to boss the assassins around is likely to result in death due to be seen as trying to pull a Goge Vandire; so the Grand Master has a lot of practical independence politically speaking. According to Lev Tieron, the post of Grandmaster is frequently behind the periods of unrest within the High Lords - Drakan Vangorich was merely the best known. That said, the recent incumbent - Fadix - was almost single-handedly responsible for saving Terra from the aforementioned coup attempt (though probably because the Custodians were too busy laughing to get involved immediately / didn't need to because their leadership knew what was going on and it let them keep their golden hands clean). Or, he goaded the seditious High Lords into showing their hands by offering them the assurance that the ultimate sanction was on their side, thereby causing the unrest and rebellion so that it could be flushed out once and for all. Fadix currently still holds the post.
• Master of the Adeptus Astra Telepathica: The guy/gal in charge of the selection, training, and use of Astropaths and other various kinds of sanctioned psykers within the Imperium. Making sure the Imperium's giant network of psychic email servers don't go to shit is so damn important to keep it running that they gave them a permanent seat.
• Master of the Administratum: The head of the Imperial bureaucracy. While the the Master of the Administratum is an equal with the rest of the High Lords on paper, in practice he is considered the "head" of the Senatorum and most powerful of the High Lords, and they are fucking territorial about that. With the Emperor appointing Roboute Guilliman Imperial Regent, the Master of the Administratum is now the second most powerful High Lord, with the Fabricator-General and Ecclesiarch now fighting for third most powerful. Irthu Haemotalion was very upset about this after being fired and got killed by Fadix along with his fellow conspirators (he was also shot by a Vindicare). He was replaced by Violeta Roskavler who has a reputation of being a hard working logistical genius.
• Master of the Astronomican: While the Adeptus Astronomica isn't nearly as large or influential as the other members' branches, they keep the light of the Astronomican burning. The Astronomican in turn keeps the Imperium from collapsing, and every other High Lord from being fucked inside out by daemons on their way to meetings, so they let this guy have a chair along with his pal/rival from the Adeptus Astra Telepathica. Because the Adeptus Astra Telepathica serves as the Astronomican's recruitment arm, having these two members disagree on policy is uncommon, but they are legally independent bodies (each of equal rank with the Administratum), so it's certainly possible. The previous one died during the Chaos (of both capital C and regular c varieties) of the Long Night and Guilliman used the opportunity to stack the High Lords with competent loyalists further after Fadix's purge of the morons who tried to rebel against a fucking Primarch already emptied several slots (along with some firings that lead to said coup attempt in the first place).
• Paternoval Envoy: Representing the Navis Nobilite, the third of the guys to get a seat because otherwise the Imperium would collapse without faster than light travel and communications. This guy/gal makes sure that the Navigators have a say in what's going on, so they won't get declared abominations of the holy human form. Unlike the other posts, s/he is not the head of the combined Navigator houses, but a representative from the Paternova, the currently effective head house of the Navis Nobilite. The Paternova cannot attend meetings because s/he stays in the Palace of the Navigators due to...changes they undergo upon assuming the post, which would cause mass rioting among the populace questions among the less-informed. As a result, the Paternoval Envoy is a young, still fully-human looking Navigator (except for the third eye, of course) and usually chosen from a weak house who couldn't upset the balance of power among the Navigators should the position go to his head. Theoretically, the Paternova's rank equals that of the other two people who run the Imperial Fleet (both of whom sometimes also get seats - see below), but they are just too practically important and significant for anyone to really claim they outrank them.

Three Dynamic Members

The remaining three fluid positions are held by people either beholden to one or more permanent members, or by people so powerful they just walk in to take a seat. Needless to say, they keep the seat as long as they, or their allies, are strong enough to hold it. They include:

• Independent
  • Captain-General of the Adeptus Custodes: He's kind of a special case: by Big. E's ancient but never overturned decree, the Captain-General speaks with His voice at all times, unless Malcador or Himself are present. This would technically make the Captain-General the leader of the Imperium as a whole (with Malcador ultra-dead and Big.E unable to communicate) but since that setup was (even more) horribly impractical, a compromise was found. In normal circumstances, The 12 High Lords and the rest of the Senatorum Imperialis deal with leading the Imperium while the Captain-General and his fellow Custodes ensure the security of the Imperial Palace and the Emperor; both institutions working in tandem without much interaction or interference. However, whenever the Captain-General decides he needs to join the discussions (for instance, to make sure the High Lords keep their shit together or to tear the next Goge Vandire a new asshole), a seat is freed for him on the spot until whatever situation made him pop his head in is resolved. While he generally despises playing politics with mere mortals whenever he does attend a meeting, all the other High Lords shut their flapping gums and pay close attention to what he has to say. NOTICE ME, SENPAI!. Not really, it is more about a Custodian being a murder machine leagues ahead of anything short of Greater Daemons, and the fact he literally has Big.E's full authority behind him. The current Captain-General is Trajann Valoris, currently the only High Lord other than Guilliman known to be getting a model and rules for the tabletop.
• Administratum Subordinates
  • Chancellor of the Estate Imperium: The Imperium's head paper pusher. Seriously, s/he's a glorified secretary. The most useless of the High Lords, and only gets on if the Master of the Administratum feels he needs another vote on things and can muscle him in. The previous holder of the office was Brach, who died in 999.M41 before the reforms of Guilliman.
  • Lord Commander Militant of the Imperial Guard: The leader of the Emprah's hammer. Nominally in charge of every man, woman, and child in the Imperium with a flashlight to point, although the bureaucratic distances and sheer, incomprehensibly large numbers of personnel involved means that s/he mostly dictates uniform and grooming standards, and maybe operational doctrine if the bigwigs at the Departmento Tactica are feeling indulgent. With the Master of the Administratum in charge of his/her record keeping and the Chancellor of the Estate Imperium in charge of his/her bank account, though, The Lord Commander Militant hasn't got as much of independent swing as one might think. Still, someone needs to give career bureaucrats some form of advice in military necessity, therefore his/her seat. The previous holder, Mar Av Ashariel, was among the failed Hexarchy plotters and was killed by a Callidus Assassin.
    • Lord Commander of the Segmentum Solar: A direct underling of the Lord-Commander Militant that often only gets a seat whenever the military situation goes from shitty to completely FUBAR and there's a need for some crusade or other to set things right a little less wrong in the Imperium. S/he is the commander of the Imperium's forces (those that listen to the military bureaucracy anyway) in charge of guarding humanity's chewy center, Segmentum Solar.
  • Lord High Admiral of the Imperial Navy: Discards the shiniest of flying space cathedrals in favour of the shiniest of desks. Like his/her counterpart(s) in the Imperial Guard, s/he often gets a seat when there is some Ork WAAAGH!/Tyranid Fleet/Black Crusade/Tau Expansion/... happening. Unlike his/her counterpart, though, s/he isn't dependent on the Chancellor for his/her money, but is dependent on the Navigator houses and the Astronomican for navigation; and on the Adeptus Astra Telepathica for communications. As a result, s/he doesn't have as much wriggling room as one might think either, but the same thing about military necessity also applies here. The previous holder of the post, Merelda Pereth, was among the failed Hexarchy plotters and was killed by a Callidus Assassin.
  • Speaker for the Chartist Captains: Spokesperson of the Merchant Fleet, this High Lord defends the interests of the various trade captains within the Imperium. They are similar to but less powerful than Rogue Traders, but make up about 90% of the Imperium's spacefaring capability. They might not look like much at first glance, but along with the various Psykers above they're the glue keeping the Imperium together by making interplanetary commerce possible at all (which is a matter of survival for many, many planets), so they too get a voice in running things when there's a seat free (read: in those times of relative calm when the military situation is galactically stable). There are four levels of Merchant Charters, from flying fixed and limited routes to being allowed to travel through all of Imperial space within the Segmenta.
• Ecclesiarchy Subordinates
  • Abbess Sanctorum of the Adepta Sororitas: The head of the Adepta Sororitas. The only member of the High Lords who is a woman by default, she is elected from the leaders of every order of the Sororitas. Like the Inquisitorial Representative, there is no real race for this position. It is, in fact, considered a penance to become the Abbess Sanctorum, which, given the other assholes in the Senatorum, is not that far from the truth. Before the Abbess is formally inducted, she is to take a pilgrimage to San Leor, the homeworld of the Daughters of the Emperor. The current would-be Abbess, Sister Sabrina of the Order of the Ermine Mantle, disappeared during her pilgrimage. Tradition dictates there cannot be another Abbess elected until the current one's fate has been determined, so the seat of the Abbess remains empty as of now. Post Great Rift, Celestine and her forces were able to find trapped fighting off waves of Daemons on San Leor. After fighting them off, Sabrina was able to take up her seat. Later, Guilliman was able to get the newest Abbess to support his purge of Holy Terra’s more corrupted dredges in society while she also urged the Assassin to send a Vindicare agent on a hunt against an Ork Warboss that had looted a Shrine-World.
  • Cardinal of the Holy Synod of Terra: Some old guy from a group of old guys who spend all their time arguing about slight deviations in doctrine. Their only useful function is electing the head of the Ecclesiarchy who gets them their chair on the council. Mentioning that this is a conflict of interest is considered heresy. The Holy Synod is an organization that primarily concerns itself with running the church on Terra, so in theory, it can provide up to 3 Cardinals to fill all the vacancies, though this would never fly even in peacetime.

The Thirteenth Lord

The position of Lord Commander of the Imperium's armed forces was one that Rogal Dorn was originally invested with as the coordinator of the loyalist war effort during the Horus Heresy. Roboute Guilliman took it from him at some point afterwards and used the title Lord Commander of the Imperium (as the first man to command the forces of the Imperium in its entirety) where it became synonymous with Lord Guilliman even past his injury and eventual removal by his brother Fulgrim (presumably because no one had the balls to remove the plaque from the door). The position lasted at least until the 32nd Millennium and was the de jure leader of the Senatorum Imperialis, and on paper was the commander of the entirety of the Imperium's military forces. We say "on paper" because the last dude prior to Chapter Master Slaughter Koorland was a puppet of the other agents of the senate, and was generally incompetent. Koorland's successor, Maximus Thane, also took the role of Chapter Master of the Imperial Fists, and was presumably the last to hold the title, because after issuing a series of standing orders, he decided to leave Terra and rebuild the broken Imperium following the War of The Beast, only returning to deal with The Beheading. The post appears to have been abolished at some point after this.

As of the closing years of the 41st millennium, Roboute Guilliman is back as the Lord Commander again, mostly because nobody else available could be trusted with a job that important, but also significantly due to the fact that nobody dared to say no to him when he announced he was taking his seat back. At least, not to his face. Several of the High Lords did, however, attempt to stage a coup, which was foiled by the Adeptus Custodes and Grand Master Fadix of the Assassinorum who had the four serving and two fired High Lords attempting the coup simultaneously killed by his subordinates. He also appointed Dante as Lord Regent of the northern half of the Imperium and as mentioned replaced the Master of the Astronomican who had coincidentally died due to the Long Night in the immediate aftermath of the Great Rift opening.

The Senatorum

As mentioned, the High Lords of Terra are a dynamic organisation, that shifts and changes according to the politics of the day. The seventeen Lords listed above in no way represent the entirety of Imperial government, nor do those Lords who don't get a seat on that particular day lose their ability to have their voices heard or impact policy; the Senatorum actually consists of tens of thousands of politicians, all with their own voting rights and agendas. However, the full body virtually never meets in session, and those positions that fall out of eminent favour simply don't occupy seats on the "High Twelve", which also comes with a reduction in privileges, including the right to give orders to Custodians (they make the distinction between High Lords and those of the High Twelve). That right to give orders, however, is rendered moot within the Imperial Palace, with the obvious exception of the Captain-General. Known lesser lords and positions are as follows, note how their jobs when described are relatively important to the general situation as well rather than being some nobody on present to raise numbers:

• Chancellor of the Imperial Senate: A rank that exists outside of the High Lords, who acts like the presiding officer of the council. Their job is sometimes more arduous than the actual High Lords, as they have to essentially herd, bully, intimidate, sweet talk, and basically cajole all 12 into regular sessions, as well making sure the process doesn't turn into an eternal game of pass the buck. They are also meant to be as politically neutral as possible, which considering how much cross intent and vested interest floats around the council is either very easy or extremely hard. Lev Tieron was the previous holder and retired during Guilliman's reforms citing old age. His protege and successor Anna-Murza Jek was instrumental in the foiling of the Hexarchy plot and is currently in office.
• Commandant of the Schola Progenium: The head of the Schola Progenium, and the joint senior-Commissar of the Imperium, presumably with the head of the Commissariat. Makes sure the new generations properly worship the Emprah and properly hate anything the government does.
• Chirurgeon-General of the Orders Hospitaller: The head Medicae of the Imperium. Though part of the High Twelve in the days of the Emperor, the Chirurgeon-General lost their status as a rotating member of the High Lords after the Horus Heresy, which goes to show how little a priority healthcare is in the Imperium, though for what its worth the post remained as major lesser High Lord.
• High Lord of the Imperial Chancellery: The head of the Imperial Chancellery. This is the person who runs the offices of the Adeptus Terra and is essentially the superintendent of the Imperial Chancellery (Custodian interference and forbidden areas of the Imperial Palace aside). Originally part of the High Twelve, it lost its status after the Heresy and remained a major lesser High Lord.
• Lord Constable of the Synopticon: The head of the Synopticon. What exactly this does is unknown. "Synopticon" is a word that means "Surveillance of the few by the many", as his title is "Constable" that presumable makes him some kind of rule enforcer for the Senatorum itself, making sure proper procedure is followed but involved in this more directly than the Chancellor? Best guess is he's the leader of the space CIA, as opposed to the Inquisition's space FBI. Alternatively, the security chief for the Imperial Chancellery.
• Mistress Plenary of the Catacombs: The person overseeing the Catacombs. What exactly that means is unknown, but given what is usually placed in the catacombs of the Imperial Palace, it probably isn't pretty.

These six are generally important to the galactic situation or at least Terra's (or the Chancellery within the Imperial Palace itself) and if any of the lesser lords outside the "can be one of the big thirteen" group are in an important but not-everyone is present level meeting its them. Other posts don't have names in the fluff at this time. Speculatively, the Segmenta and particularly important Sectors might have representatives.

When it is expedient or politically advantageous to do so, the High Lords may choose to take seats in various chambers around the Imperial palace. While some chambers are large enough to seat the whole of the senate and then some, others are barely larger than an office, where lesser lords get excluded (save the above posts who as mentioned previously are the most likely of the lesser lords to be present in big deal government meetings which involve those outside the High Twelve but not the other Senatorum politicians, alongside the rotating greater lords).

Finally, the actual bureaucrat in charge of the Senatorum itself, the Chancellor of the Imperial Council (currently Anna-Murza Jek, protege and successor to the retired Lev Tieron), should be detailed further. This is not a High Lord of Terra, but still wields great political power as being in charge of the top level bureaucracy allows them great influence and power as was seen when Jek became suspicious of the fired Master of the Administratum and Ecclesiarch plotting against Guilliman. She was critical in arranging for the traitors to spring their coup early and getting them killed by Grand Master of the Assassins Fadix backstabbing them.

Trivia

• The authors of the Horus Heresy series are collectively referred to as the "High Lords of Terra" on Black Library's blog. According to Dan Abnett, this is intended as self-deprecation. Yes, even the makers of 40K canon think the High Lords of Terra are useless.
• All tea and biscuits are the property of the High Lords of Terra and no one else. They are needed for the constant meetings the High Lords have (most likely to decide what colour to paint the Imperial Palace's walls this season).Of course it should be GOLD, the Emprah's favorite!
• The High Lords do decide on foundings of Space Marines and assign the title of Warmaster to special individuals undertaking Imperial crusades. However considering how many chapters turn renegade or do their own thing and how many crusades seem to fall into failure, this could be further proof of the High Lords' collective uselessness.
• With Papa Smurf as defacto leader of the entire Imperium again, the usefulness of the High Lords have went up a reasonable notch. Mostly because most of them were sacked and replaced after they were dumb enough to try and stage a coup against Roboute freaking Guilliman.
• Their Fantasy equivalent, the Council of Thirteen manages to be more effective and productive despite being run by megalomaniac backstabbing ratmen drug addicts.

See Also

• Writefaggotry from /tg/ on the High Lords