In the backstory of the Warhammer 40,000 universe is humanity's era of hope, only just starting to dawn after the long and terrible Dark Age before being brought to an end by the Horus Heresy, wherein fully half of the best warriors the human race had to offer turned to worshipping dark gods and nearly wiped out the other half. The God-Emperor was permanently injured in a lethal duel with their leader, Horus (his son, in a way), to the point that he is only kept alive by an extremely complex life support device.Long established in the background as being directly responsible for the shape the galaxy is in in the 41st millennium, it is the subject of the Horus Heresy series of novels and audio books, by various authors.While the concept of finally fleshing out a canon backstory for 40k originally excited many long-time fans, the series has been met with widely varied opinions from its fanbase. The series is however the Black Library's most popular, with new titles regularly appearing in the New York Times best seller list.The series consists of:
Repeatedly. Just in the backstory, Earth had been rendered all but utterly inhospitable to life due to centuries of nuclear/chemical/biological (with a little sorcerous) warfare during the isolation of the Age of Strife; if the Emperor hadn't shown up when he did it most likely would have continued on and been left a burned-out lifeless rock. Then we get into all the OTHER planets that went through cataclysmic eras during that time, nevermind those that were completely obliterated on purpose.
Alien Geometries - The Laeran Temple, the entirety of the Furious Abyss, the Eldar, etc.
Lets not forget the tomb of the Dragon beneath Mars in 'Mechanicum'
Subverted in The Reflection Crack'd when Fulgrim turns the tables on the Daemon and regains his body, trapping the Daemon in the painting. Unfortunately he's become even worse than the Daemon and is completely evil.
Annoying Arrows - Subverted to the Warp and back by the Interex, whose primary weapon is a technological bow... which can shoot an arrow straight through a Space Marine in full armor. Played straight when Horus gets hit in the arm by one and pulls it out casually, though.
Arc Words - Played with a bit. Because most readers of the Horus Heresy books will already know what's going to happen and have an omniscient view of the storyline they will know that "I can't say" is the challenge/answer phrase for the secret Lodges. Every time it is used, it always refers to clandestine lodge business that is not for the ears of outsiders. Then in Nemesis Constantin Valdor utters, in a completely different but equally clandestine context, "I can't say", reinforcing the theme of shadow wars and intrigue occurring in the background.
Samus is watching. Samus is all around you. I am Samus.
In later stories the phrase "The Emperor Protects" takes on hidden meaning.
In A Thousand Sons and Prospero Burns we have "There are no wolves on Fenris."
Attempted Rape - Serena D'Angelus makes an excuse to Lucius that she was about to be raped by the now-dead guy on the ground next to her. Lucius shrugs it off.
Badass Boast: I am the Storm's Blade, I am Justice, I am Defiance and I am the Oath Keeper! Cerberus, Legion Of One
Badass Normal: Possibly the most Badass Normal in the entire history of 40K is Dinas Chayne, a totally normal human who was able to fight on level with a 8 foot tall, genetically engineered, super soldier...and wound him. Pity that he got his sword stuck in Captain Sheed Ranko's/Alpharius chest though...
Wait, don't forget Peto Soneka and Hurtado Bronzi! The story is almost completely about them.
A mild example would be that of the Priest in the short story "The Last Church". He openly defies the Emperor, willingly choosing death rather than walk off personally with the Emperor.
Let's put this one in context. This is an old man, alone in the last Church on Terra. He is surrounded by proto-astartes. And after the Emperor has spent the last hour trying to destroy his faith via argument, he defies the Emp to his face.
Which is hilariously ironic given it was the Emperor who unintentionally inspired his faith in the first place and therefore not even the being he thought was God, telling him not to believe could break his faith.
Bad Dreams - Par for the course, but Horus' are particularly nasty.
Batman Can Breathe In Space: In Know no Fear Roboute Guilliman gets knocked off his flagship's bridge into space and without a helmet by a daemon attack. It's actually in low enough orbit that there's a very thin atmosphere, which is enough for the primarch to survive for several hours and then still have enough stamina to punch some Word Bearers to death.
Bearer of Bad News - Garro who imparted it unto Rogal Dorn, who imparted it unto the Emperor.
In The Outcast Dead. Kai Zulane, after finally removing the mental block in his own psyche, tells the Emperor that he is going to die. Subverted in that the Emperor already knew this.
Cain and Abel - Rather than a single case, it's essentially half a fraternity of Physical Gods becoming the Cain to the other half's Abel.
Call Back - Throughout the series. For example in The First Heretic, Argel Tal, during his trip in the Immaterium with Ingethel, gets to visit the labs of Terra as the Primarchs are being grown. Which appears to be the same scene Horus will be subjected to on Davin, fourty years later, in False Gods.
Combat Pragmatist - Loken, when challenged to a sparring match by Lucius, starts and finishes it by punching him in the face. He did warn Lucius that the match wouldn't just be about the sword.
Conflicting Loyalty - A few marines suffer from this: who first, their Primarch or the Imperium?
Continuity Nod - The authors seem to have a contest as to who can put more of these per-book than the others.
Prospero Burns: We meet a Space Wolf called Bear. His arm is destroyed by a daemon during the scouring of Prospero and replaced with an augmetic. Shortly thereafter we learn that his name is actually Bjorn; indicating that this is actually Bjorn the Fell-Handed, who would go on to become the most famous Dreadnought and the oldest loyal Space Marine in the 41st millennium.
In the Age of Darkness story "Rules of Engagement", an Ultramarine Captain thinks it will take something far greater than Traitor assault to destroy the beauty of Prandium. Ironic when you consider it gets nommed by Tyranids.
Cultured Warrior - The Emperor's Children take this to the point of arrogance. The Thousand Sons as well—preserving libraries and knowledge (particularly of sorcery, but all subjects are considered important) is a primary goal to the point it brings them into comflict with the Space Wolves, and individual members have hobbies like philosophy and winemaking. Horus and his Mournival also fit the bill pre-corruption.
Dead Person Conversation - Horus' time in the Temple of the Serpent Lodge, he speaks to one of his senior captains who had died in the events leading up to Horus Rising. Though, subverted, because it was Erebus disguised with sorcery, although the readers practically know this by the time it occurs.
Disproportionate Retribution - The Emperor's rebuke of Lorgar proclaiming him as a God was the cause of his fall to Chaos, but The First Heretic shows just what that rebuke entailed: ordering the Ultramarines to destroy the city of Monarchia, which exemplified the Word Bearers accomplishments, then ordering Lorgar and the entire Word Bearers legion to kneel before the Emperor, Roboute Guilliman, and Malcador the Sigilite in the city's ruins as they re-pledged themselves to the Great Crusade. Even the other Primarchs thought it was excessive. Is it any wonder that the Word Bearers betrayed the Imperium?
There are many occasions in the first few books when the characters consider scenarios like Astartes fighting Astartes or Horus trying to take a fortress defended by Rogal Dorn before dismissing them as impossible.
The end of Fallen Angels shows Lion innocently handing over the engines, which he defended from Horus, to Perturabo.
Nathaniel Garro would have died on Isstvan Extremis before carrying news of the Heresy to Terra if he hadn't received emergency medical treatment from Fabius Bile, of all people. Doubtless he would have ignored Garro (or put a surreptitious bolt in his head) had he any inkling of how much trouble he would be.
Dramatis Personae - Every book has one or two pages listing the main and peripheral characters. Thankfully, they don't spoil much.
The Federation: The Interex come off as this compared to the Imperium, which is already showing signs of being The Empire. They're a highly technologically advanced society who cherish peace and are willing to extend the hand of friendship to aliens; not only is their society literally built on a centuries old alliance with a once-dying alien race called the Kinebrach, they defeated the disturbingly Tyranid-like Megarachnids and chose to simply strip them of space-faring capabilities and imprison them on an otherwise uninhabited world around which they posted warning beacons, as opposed to simply massacring them. One interex character, when questioned about this, proclaims that they had no right to annihilate another species just because it was different. Furthermore, they are well aware of the dangers of Chaos and regard it rationally and openly as a threat that must be opposed by all sentient beings. In fact, they are hesitant to embrace the Imperium because they see its brutal, war-like ways and fear it is already tainted by Chaos. Naturally, they are plunged into war with the Imperium and utterly destroyed by it.
The Fettered - Zahariel, Tarvitz, Loken, most other non-traitors (and a few of those as well).
Fire-Forged Friends - The best way to get Astartes of different Legions to bond is to have them kill people together. Aww.
First Name Basis - The Astartes were actually friendly in Pre-Heresy times. Well, some of them were, anyway.
Five Rounds Rapid - quoted as a Shout Out in Fallen Angels, used in spirit in a number of other places, usually when a new Legion first faced Chaos-based nasties.
Foregone Conclusion - virtually every single major event in the entire series. What makes it interesting is the few loyalists who remain in the Traitor legions, and the characterisation of those characters who had previously been relatively one-dimensional villains.
The whole of the Horus Heresy itself. We all know how this ends.
God Emperor - Constantly talked about, rarely featured directly. When he does make an appearance, it's often a eerie yet awe inspiring experience for those involved.
The Good Chancellor - Malcador the Sigillite, mentioned in passing in game materials, finally appears here. The Emperor's right-hand man, he plots on a level that would make Lord Vetinari jealous, while holding everything together day-to-day.
Gone Horribly Right: Loken tells Karkasy to tell the truth, no matter how ugly and horrible it is, in Horus Rising. By False Gods, Karkasy is still telling the truth, as ugly and horrible as it is, by pretty much slandering the Imperium and supporting an outlawed cult. Horus has Karkasy killed for it.
Hero with Bad Publicity: Pretty much the entire Sons of Horus legion in False Gods after they trample a crowd of innocent people when they're consumed with rage and grief at Horus being severely wounded by the anathame.
Don't forget Iacton Qruze, who not only was one of the few Sons of Horus loyalists, but actually renamed his men back to Luna Wolves, and after escaping to Terra became one of the first Inquisitors together with Garro.
It's All About Me - Horus, again. The Primarchs seem to have this as a trait generally though.
It's All My Fault - Horus blames himself when Angron's attack throws off his plans in Galaxy in Flames.
Horus was like this a lot in Horus Rising. Unfortunately subverted at the end of the novel, when things go to hell, claiming that it wasn't his fault (which it wasn't) decided he had enough and killed everything.
Special mention to a side-revelation in Mechanicum. Forget Chaos for a moment. Those puny bastards have only been around for a few tens of thousands of years. Sol, the heart of the Imperium and cradle of humanity, is home to the Void Dragon, a C'tan star god that could eat the Sun if it woke up on Mars. But it gets better still - the Void Dragon is the Machine God that the Mechanicum, essentially humanity's technological backbone, unknowingly worships, and its primary aspect is complete control over technology. And the God-Emperor who beat it up in the past is now on life support so even if he wasn't getting played all along by a nearly all-powerful, billions of years old God, he can't do a thing to stop it now. And this is a back burner problem.
Oh, yeah, and the method of keeping the Void Dragon sealed is probably lost forever because one of the party in Mechanicum stole the book needed to teach the Dragon's next keeper what he needs to know to do the job. Generally, people figure Zouche was the Deceiver in disguise.
It Was a Gift - Every important Space Marine has one or two of these. Primarchs have them up the wazoo. They vary in importance from "offhand mention" to "will be referenced in another book" to "major overarching plot point".
Kick Them While They Are Down - The traitors do this a lot. Eidolon's attack in Galaxy In Flames intentionally starts with the wounded and The Medic. Lucius does it to Solomon Demeter in Fulgrim.
Lighter and Softer: As amazing as this trope may seem, the earlier books in the Horus Heresy are much less Grimdark than the books later in the series and much, much lighter than the books taking place in the 41st millenium.
Meaningful Rename - Legions were renamed by their primarchs in the Back Story; the betrayed Sons of Horus (briefly) call themselves the Luna Wolves again; and Abaddon renames the Sons of Horus, to the Black Legion, at the end.
My Eyes are Up Here - Euphrati Keeler says this trope almost word-for-word to Ignace Karkasy in "False Gods"
My God, What Have I Done? - Fulgrim suffers this at the very end when he kills Ferrus Manus. It is said that Horus would have had one if he had taken over the galaxy like he planned.
In fact Horus did have one during his climactic duel with the Emperor during the Siege of Terra. In the brief moments before he was completely obliterated by the Emperor's psychic onslaught, the man Horus once was came back and he basically had time for this trope, followed by "I'm sorry"... and then he dies.
Partially subverted and averted in Ages of Darkness. A loyalist Thousand Son attempts to "heal" (using his physic powers to show him how wrong his actions were) Equerry Kharn of the World Eaters. He fails, but his last revenge before Kharn kills him is the knowing that Kharn will forever live with the knowledge that his betrayal was wrong (and that he could willingly have turned back). He then wonders what effect this will have on Kharn in the future...
A small side note; In the Great Crusade and Horus Heresy, Kharn was the comparative voice of reason and calm to his primarch. He only gained his reputation for being a tad touchy AFTER the heresy was over...
Not so much in the Heresy. Right after the Betrayal at Istvaan he's seen as a slavering lunatic, roaring about the Eightfold Path. This madness-on-the-edge-of-control continues into Age of Darkness' "Rebirth" where he's acknowledged as being changed into an utter madman, consumed by bloodlust.
This is presumably Khorne's little joke: the Blood God would probably be amused by the idea of turning the Legion's most restrained, stable and level-headed individual into a raving lunatic, if he wasn't so bloody furious all the time.
Could verge into Fridge Brilliance. Khan's team killing tendencies could be partly the result of being unable to mentally reconcile a berserker mentality with genuine guilt.
Arguablly The Emperor is guilty of this with his 'rebuke' of the Word Bearers and Lorgar. As pointed out in Novel its not like their religious aspect was anything new, So why wait so long to bring them to task. And of course in such a public humiliating way to? Hell the fact that Magnus AND RUSS of all people agreed that the rebuke was a bad idea should have been a big clue!
The Emperor, again, this time with a good deal less doubt about it. He made sorcery illegal, which Magnus the Red and his Thousand Sons legion reluctantly accepted. However, when Magnus foresaw Horus' betrayal, he broke his promise and contacted the Emperor directly via sorcery. The result? The Emperor sends Leman 'I Hate Written Knowledge' Russ to apprehend Magnus on Prospero, better known as the greatest library in the universe after the Black Library. Russ and company believe that the warning was an attempt by Magnus to scare the Emperor into allowing sorcery again, and proceed to destroy Prospero and force Magnus to turn to Tzeentch to save what remained of his legion.
Interestingly, in the exact same situation, Magus, since his warning obliterated The Emperor's work to open a gate way into the Webway, which would have allowed humanity to never have to use the Warp again.
It wasn't just sorcery, but all aspects of psykerism with the exception of Navigators. At Nikkea several Chief Librarians of other Legions spoke on Magnus's behalf to attempt to sway the Emperor's opinion because of how important psykers were to the Imperial war-effort. And of course we later learn the destruction/corruption of the Thousand Sons was a key aspect to the Heresy specifically because their psychic powers a huge threat to the Chaos Gods and their forces.
The Emperor does seem to be holding a huge Idiot Ball at most points in the storyline. His plan for dealing with Chaos is to lie to and woefully under inform all of his sons, and his entire population, about what Chaos *is* (telling Horus, for example, that chaos "demons" are just random collections of emotions that have no real intelligence or guiding force), apparently completely forgetting that one of the major powers of Chaos literally plays chess with mortals. He didn't once think that the chaos gods would try to tempt the primarchs? And that his lack of instruction on them would leave them largely defenceless? Really, this combined with the above examples demonstrate that the Emperor is either a huge idiot or he was actively attempting to end up on the Golden Throne.
Nice to the Waiter - Hor-...oh, you can guess. Well, to start off with he's nice, anyway. Otherwise, a good sign between the good guys vs. the bad.
No Hero to His Valet - Subverted - Every heroic figure is held in high esteem by all, except for the main characters. This is particularly exemplified when a Legion's Space Marines generally have such a lofty opinion of their Primarchs that it borders (and crosses into) fanaticism.
Not As You Knew Them - In 40K the Space Wolves are one of the nicer chapters in their relations with normal humans, especially civilians. During the Crusade, their reputation for ruthlessness, superstition and savagery against their foes made the Vlka Fenryka the most feared force in the galaxy, with some Imperial Army units considering defeat preferable to calling the Rout for help.
Not Quite Dead - Maloghurst and Horus both turn up alive after their deaths seemed apparent.
As of the Audio Book 'Legion of One', it is confirmed that Garviel Loken is this too, as the Warrior Cerberus
Not So Stoic: Roboute Guilliman is ordinarily the most level-headed, intellectual primarch. But when he learns the depth of the Word Bearers' treachery at the Battle of Calth he swears to kill Lorgar personally, even after admitting that it's not the best move tactically.
Obfuscating Stupidity - Space Wolves: Brutal, brain-dead Proto-Vikings in Space who do nothing but destroy in an uncontrollable fury? Nope - highly trained, ruthless, utterly unfettered battlefield analysts designed to kill another Legion, as The Emperor's Executioners
Oblivious to Love - Serena D'Angelus, because she's wrapped up in being corrupted by Slaaneshi influence.
Old Retainer - Every Legion has at least one. They vary in plot importance and even background from book to book. Malcador is this to the Emperor.
One-Man Army - If normal Space Marines are this to humans, the Primarchs are this to Space Marines. We don't get to see it that often, but when the Primarchs let loose, they can be terrifying indeed.
Angron in Galaxy In Flames: After virus bombing Isstvan III fails to kill the Space Marines who would have stayed loyal, Angron leads an assault force of the World Eaters and starts by tearing up his own former Legionarries. The assault is so violent that Saul Tarvitz, a Space Marine, actually runs away.
In A Thousand Sons, when Azhek Ahriman meets Leman Russ for the first time, the sheer amount of aggression emanating from Russ's aura is so strong it causes Ahriman a minor Brown Note and he has to cut himself off from the warp for a moment to keep from going nuts.
Corvus Corax in The First Heretic: He takes on a small army of Word Bearers who have been possessed by daemons and cuts through them like they're paper.
Roboute Guilliman in Know No Fear: Fights for several hours on the hull of his flagship while in orbit low enough to have an atmosphere so thin only another Primarch could survive unhelmeted. All the while, he's killing Word Bearers on the hull with only his power fists.
Only Sane Man - The protagonists of each novel get to watch as things go to hell around them.
Our Dragons Are Different - The Void Dragon, locked under Mars by the Emperor after he found it weakened on Earth. Being C'tan, the only reason it's even called a "dragon" is that it chose that form on Earth.
Unfortunately, Chaos isn't strengthened only by active worship, being as it is the collective embodiment and manifestation of the emotional output of every sentient being in the material universe, so the Imperial Truth wasn't starving Chaos as it was intended so much as reducing its servings slightly. Turns out the only real way to counter it is with an alternative object of worship.
Or to push a secular worldview that admits that there are entities in the Warp, strips them of all their mysticism and openly explains what they are, why they do what they do, and how they operate. Thus was the culture of the interex, who did a much better job of holding out against the Dark Gods than the Imperium did under the Emperor's direct guidance. Case in point, they fell only because one of the Word Bearers (already corrupted to Chaos by that point) used Horus's first contact diplomacy as a way to sneak in and provoke a war between the Interex and the Imperium, which the much more warlike and much more brutal Imperium, naturally, won.
Parental Favoritism - The Primarchs all have their rivalries, their favourites, and the Emperor does as well.
Personal Effects Reveal - Horus Rising when Captain Loken finds a lodge badge; The Flight of the Eisenstein, when Garro goes through Kaleb's possessions.
Place Beyond Time - The Immaterium and Horus' visions during his time in the Temple of the Serpent Lodge.
Posthumous Character - The only immediate conclusion that can be drawn about primarchs 2 and 11. They are mentioned several times, but characters talking about them are either interrupted by other characters or stop conveniently short of revealing something important about why they are not around any more.
The series is also sprinkled with hints about what may have happened to them and their legions. Leman Russ implied that the Space Wolves had been ordered on to fight another legion before the burning of Prospero and an operative of the Vindicare temple has been called on to eliminate at least one "Brother Captain".
There are even theories given in universe. The most popular one is that the two spare legions were subtly dispersed into the Ultramarines, explaining why there were so many of them.
The Power of Friendship - A few friendships made cross-legion prove to be stronger than the marines infamous loyalty to their Primarch.
Power of Trust - A running theme through the series, and a big part of the opening trilogy is just who the loyalist marines can trust.
Praetorian Guard - The Custodes killed by Horus in False Gods. Mortarion's Deathshroud, too, in Flight of the Eisenstein. And Fulgrim's Phoenix Guard, and Ferrus Manus's Morlocks. It seems most of the Primarchs (though by no means all, Horus doesn't, for instance) have some form of Honour/Praetorian Guard.
Pyrrhic Victory - At the end of Galaxy in Flames, Loken and company make damn sure Horus's victory costs him.
Rebellious Rebel - Cutting this off was the reason for the Isstvan V attack — and fomented it among the survivors. Also Garro, and the crew of the Eisenstein.
The Resenter - The Primarchs all have their shortcomings. Most legions resent the prissyness that the Emperor's Children exude. Several primarchs resent Horus' ascension to Warmaster status. Half of the primarchs resent the Emperor. Fellow Death Guards resent Garro. It's quite common.
Sibling Rivalry — Present among the Primarchs. When Horus was appointed Warmaster, he believed that only Sangiunius, Rogal Dorn, Fulgrim, Mortarion, and Lorgar geniunely supported the decision, with the other doing so reluctantly. Petronella Vivar was shocked when Horus told her this, but he responded that they may be family, but they're still siblings, and all siblings try to outdo the other to impress their parents.
There are also more casual examples. The Lion and the Wolf had a particularly violent spat over engagement procedure. Dorn and Perturabo had a...disagreement about the defensibility of the Imperial palace (oh irony). Roboute Guillman, Paragon of the Standard Procedure, outright denounced Alpharious, Master of the Unorthrodox and Decentralised leadership.
Sinister Minister - In the backstory, Cardinal Tang, who is Hitler in the distant past/far future of the 29th Millennium.
A Storm Is Coming - Before the occurrences of Isstvan III's destruction, the warp is turbulent and heralds a great turbulence in reality. Also, you'd be an idiot not to see this coming.
Super Soldier - Considering that this is the age of the Space Marine Legions, this is emphasised a lot. However, the Primarchs exceed all expectations and then some.
Even more scary are the Proto-Astartes. Not a lot is known about them, but the two that survived up to the Horus Heresy were considered badass even by Space Marine standards. Whilst the Space Marines were created with the idea of being an elite fighting brotherhood united in arms for the good of mankind, the Proto-Astartes were brutal borderline psychopaths with loyalty solely to the Emperor. Who repaid them with a bloody post victory pogrom after the conquer of Terra.
Took a Level in Jerkass: While generally considered a moral paragon by the standards of Warhammer 40,000, the novels show that the Emperor was a bigger prick than anyone realized. Most notable in The First Heretic. It was established that The Emperor chastized Lorgar for his religious zeal, but what wasn't established was how he made his point before doing so. He ordered the Ultramarines to completely wipe out a complacent city that the Word Bearers had converted to his worship. These people had done nothing else, but were destroyed solely to provide an example of what would happen to those who engaged in religious practices. Similarly, Horus' sorrow and growing insecurity are over the Emperor up and leaving, going home to Terra and telling him, his favoured son, absolutely nothing about why. In Mechanicum, he appears on Mars, demands the planet's allegiance, seals a tomb of ancient technology and erases the Fabricator-General's memory of where it is - but not, for some baffling reason, his memory of Emps being a giant dick to him. Guess who led over half of Mars into rebellion a couple hundred years later? Emps really did not stop to think too much about how ordering people to do things and never telling them why might turn out in the long run.
�bermensch - Magnus the Red is determined to be this.
The Un Favourite - Nobody likes Perturabo. Konrad Curze is also like this, as well as Alpharius to an extent, due to their sneaky, secretive natures. Although to his credit, Alpharius doesn't give a damn in the slightest.
The Unfettered - It doesn't matter what The Emperor asks, The Rout will carry it out.
Unfriendly Fire: False Gods has a particularly nasty example which is only revealed after the act due to the chaos of battle, when Horus has the army leader killed.
This was originally an in-joke on the part of the developers, as "vanus" is latin for "empty", meaning that in the 41st millennium, there was no 6th temple.
Was It Really Worth It? - Usually, if asked this, most Traitor marines reply with "Yes" and a bolter to the face. Implied by the Eldar that, were he to win, Horus' grief and remorse would overcome him, causing him to declare war on...pretty much everyone left, in shame.
and, perhaps most disturbingly of all, that Horus going mad with grief and slaughtering the ENTIRE Imperium of Man... would be the best possible outcome of the Heresy!
Kai Zulane: But you're going to die. The Emperor: I know.
Wicked Cultured - Horus is a nice guy. Fulgrim is a patron of the arts. Magnus really likes books and libraries. Lorgar is said to be at heart more visionary and philosopher than warrior, as much as a guy with a giant spiked mace can be.
Woobie Destroyerof Worlds - Of all people, Angron. Seeing him reminisce about his comrades who just recently died, punctuated by groans of despair, is pretty heart-wrenching.
Words Can Break My Bones - Warsingers, to an extent; they use their (heavily implied to be Slaaneshi-given) powers to create deadly magical effects through their singing. Also, Eidolon and the Noise Marines.
Invoked in Prospero Burns, where in a flashback we are re-introduced to Abnett's reality warping proto-language, Enuncia. Using it murders someone and causes the invoker to bleed from the mouth
Would Not Shoot a Civilian - Initially played straight, although as the books go on, they're beginning to get gleefully subverted. Especially during the virus bombing of Isstvan III. They ARE Space Marines, after all. Rather brutally subverted by the World Eater / War Hounds Legion. Angron is depicted pretty consistently as rather undiscriminating when choosing targets.