In the backstory of the Warhammer 40000 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:
A Form You Are Comfortable With - The daemon in Prospero Burns says that its true form would drive Kasper Hawser mad, so it uses Horus', Amon, the Thousand Son, and Navid Murza's forms instead. Strangely, it had planned on killing Kasper, so why it was worried about this is a mystery.
After the End: The Warhammer 30k era is essentially Humanity rebuilding itself after it's first empire collapsed. Whether this was ultimately a good thing or not, well...
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 (though he burned his share of places). Then we get into all the OTHER planets that went through cataclysmic eras during that time, never mind those that were completely obliterated on purpose.
A Good Way To Die - All Space Wolves want this and want to be remembered for it. It's not that they want to die. It's that they want to die fighting.
Alien Geometries - The Laeran Temple, the entirety of the Furious Abyss, the Eldar, etc.
There's also the tomb of the Dragon beneath Mars in 'Mechanicum'.
All According to Plan - The daemon that possesses Kapser Howser basically tells him this about the Thousands Sons' and the Space Wolves' conflict.
All of the Other Reindeer: Some Primarchs were this way before they were rediscovered by the Imperium, due to just how different they were to vanilla humans. Some of those who would turn traitor were still suffered from this because of how they were radically different to the ideal the Emperor had in mind for them.
Amazon Brigade: The Sisters of Silence, composed entirely of Blanks, are a prototypical form of the Sisters of Battle.
A Mechby Any Other Name - Dreadnoughts and Titans play a big role in the story. Martian Knights bridge the gap between the two.
A Million is a Statistic - In Prospero Burns, the Space Wolves drop Quietude graving dock onto the planet below. The Wolves response: howl, shout, and shake their fists. The Imperial Army Leader's response: To chew out Leman Russ for destroying the electronic data and knowledge from the dock.
Anachronism Stew - Melee weapons are prevalent in the 40K universe, as backups and as preferred weapons by some forces. 30K is no different.
Astartes use melee weapons include ye olde axes. The over of Prospero Burns shows a Space Wolf with a freakin' wooden buckler.
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.
And Show It To You: In Know No Fear, Roboute Guilliman tells Lorgar that he's going to rip out Lorgar's heart and show it to him. He ends up doing it to Kor Phaeron instead.
Animorphism - Some Space Wolves "fall" and become giant wolves. Psyker abilities can force this change on a Space Wolf.
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.
Anti-Magic - Blunters, blanks, and pariahs, including the Silent Sisters who are a military force composed entirely of blanks.
The Culexus assassins are trained exclusively from Pariahs, the strongest anti-psykers produced by humanity.
Apocalypse Wow - In Prospero Burns, the Space Wolves drop a graving dock onto a planet, making a continent sized crater. Also, they use plasma energy, las bombardments, kinetic munitions, gravity bombs, targeted missiles, magma bombs, and atomic bombs on Prospero. It is hinted at that the bombardment created NEW FAULT LINES!
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."
"Let the galaxy burn." 10,000 years later, the Traitor Legions are still following Horus's orders.
"The Mark of Calth" is becoming one for the Ultramarines, essentially becoming their version of Never forget.
The Kinebrach Anathame deserves special mention, being a magically-crafted weapon and the sword that wounded Horus and set him up for his fall to Chaos. And it's not done doing horrible things yet.
Artifact Title - While the Warhammer part of the title was already an artifact around the 2nd edition of the tabletop game, in the context of the Horus Heresy series, the 40,000 part of the title becomes one as well, as it takes place around 30,000 AD.
Artificial Limbs - This being Warhammer 40K, this isn't a surprise. It is mentioned Bear will get one after Prospero Burns.
Attempted Rape - Invoked Trope. In Fulgrim, Serena D'Angelus makes this excuse to Lucius, lying that the remembrancer she murdered, was killed in self-defence because he was about to rape her. To really hammer in how the legion is falling in on itself, Lucius shrugs it off, telling her that he would send somebody in to clean up for her.
Authority Equals Asskicking - More or less a requirement for being the First Captain of a Space Marine Legion. Ezekyle Abaddon of the Luna Wolves/Sons of Horus, Sigismund of the Imperial Fists, Raldoron of the Blood Angels, Sevatar of the Night Lords, Jubal Khan of the White Scars, and Gabriel Santar of the Iron Hands are all considered the best warriors of their respective Legions. Even the more intellectually inclined Legions First Captains, such as Ahzek Ahriman of the Thousand Sons and Ingo Pech of the Alpha Legion, are noted for being formidable warriors. Kor Phaeron as First Captain of the Word Bearers is a notable subversion of this trope.
Awesomeby Analysis: The Ultramarines have this as their hat, in addition to ruthless efficiency and peerless discipline. But especially Sergeant Thiel who recognises that bladed weapons and flames work better against Daemons because of their ritual significance, and also works out the ingress points on his ship that the Word Bearers would use.
Axe Crazy: Angron has "butcher's nails" implants in his skull that drive him with constant pain and aggressive urges. This coupled with his perpetual anguish over how the Emperor basically made him watch his best friends die, makes him utterly incapable of relating to (relatively) normal human beings. This coupled again with how the Nails keep him from any restive sleep further contributes to his insanity, and the combined exhaustion is slowly killing him. Nevertheless, the World Eaters willingly take the same horrible implants (a much, much less severe version, of course) in order to gain an insight to their Primarch's character and to better relate to him. In essence, they seek kinship with their father by breaking themselves on the same anvil upon which he was shattered. It's quite beautiful, in a twisted way...
An Axe to Grind - Fensian Space Wolves like to use axes in combat, and World Eaters prefer to use chain-axes.
Awful Truth: In The First Heretic, Lorgar and the Word Bearers discover the "Primordial Truth" of Chaos, where Ingethel says that those who accept the Chaos Gods will be taken into their power, while those who reject them will be cast out and eaten by daemons, and that the Emperor created the Imperial Truth to deny Chaos and damn humanity to stagnation. Just one problem: Ingethel was lying. In Deliverance Lost when a Word Bearers ship pulled into the Warp by the Raven Guard, the crew, both human and Word Bearer, gets eaten by daemons. The Chaos Gods literally don't care what happens to those who worship them.
Badass Boast: I am the Storm's Blade, I am Justice, I am Defiance and I am the Oath Keeper! -Cerberus, Legion Of One
Now? Now Prospero falls. -Leman Russ, Prospero Burns
Badass Bookworm - Kasper Hawser is remade by the Space Wolves. They give him super strength, youth, fast reflexes, and an eye that uses night vision. Without any training in fighting , he takes out several Imperial Guardsmen without breaking a sweat.
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 though...
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 to personally walk off with him..
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.
Fulgrim is, so far, the only Primarch that's flat out won in his every appearance. While every other Primarch is off fighting his own petty battles, Fulgrim gets the first Primarch kill of the Heresy, fights off a demon who possesses him, has the first legion to successfully convert to recognizable Chaos Marines, and becomes the first Primarch Daemon Prince.
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.
Battle Cry - The Space Wolves makes snarls, roars, and "leopard-growls".
Battle in the Center of the Mind - An unusual case Kasper Hawser's mind was being altered by a daemon. He couldn't fight the beast and he could only regain his memories by altering his dreams. Space Wolf Rune Priests attempted to help him fight the being, but one of them was turned into a wolf. This priest claimed Horus turned evil. Later on, Kasper walks into a room and into the room that he is in in his dreams. The daemon combined the two realities. Therefore, it was a battle in the center of the mind outside of the body. It took the arrival of a Rune Priest, two dreadnoughts, and two dozen Silent Sisters to beat it back.
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.
In Fear to Tread the Blood Angels find ships that tried to flee from Signus Prime that lacked warp-engines, meaning that the people knew they were going to die in space. Being Astartes, they're mystified as to why anyone would do that, until the Shipmistress of the Red Tear explains it: whatever was happening in the Signus Cluster was so terrifying that they willingly chose death in the void over being kill by the invaders.
Big Badass Wolf - Prospero Burns has plenty... then again, there are no Wolves on Fenris...
Big Damn Heroes - At the end of Know No Fear when Captain Ventanus and the 4th Company are on the verge of being overwhelmed by Hol Beloth when reinforcements show up. And by reinforcements, we mean the 19th company under Captain Aethon, the remnants of the 111th and 112th companies under Sergeant Anchise, three Titans under Tetrach Tauro Nicodemus, and Army forces under Tetrach Eikos Lamiad. And they are pissed.
Eada Haelfwulf and Ulvurul Heoroth, AKA, Longfang in Prospero Burns. Also, Thousand Son Astartes and the daemon bleed from the mouth, well as other orifices, when confronted with powerful marks of aversion and pariahs.
Blood Magic - Aside from the obvious Chaos-related nastiness, the Black Cube that the Nurth possess requires the deaths of hundreds, even thousands, of people to be activated.
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.
There are also specific cases between individual Primarchs. Most notably, Perturabo is the Cain to Dorn's Abel; then there's Russ, theloyalist Cain to Magnus'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.
The Chosen One: Several. Including the Emperor, who is sometimes cited as having been destined to rule humanity in the meta sources. And then there's Horus having become the Chosen One of the powers of Chaos, reminding us that this trope isn't always a good thing.
Combat Pragmatist - Loken, when challenged to a sparring match by Lucius, starts and finishes it by grabbing his sword arm and punching him in the face. He did warn Lucius that the match wouldn't just be about the sword.
Compelling Voice - Combined with Trigger Phrase in Prospero Burns. A daemon could hurt a person with magic if it knew the person's name. These names were stolen from Kasper Hawser's mind.
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.
Ironically, though becoming a Dreadnought is considered an honor, Bjorn was happy when he only lost an arm instead of being forced to become a Dreadnought. Obviously, his luck didn't hold out.
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 eaten by Tyranids.
In Nemesis Siress Callidus wants to deploy a new Callidus assassin to kill Horus. The assassin's name? M'shen, the woman who assassinated Konrad Curze.
Virtually all the major Iron Warriors players in Storm of Iron appear in Angel Exterminatus.
Continuity Snarl: McNeil does one against himself. A third of the way through The Outcast Dead we see The Emperor receive the ill-fated psychic warning from Magnus, which leads to the Space Wolves going to Prospero for some smashy-smashy. The book says this takes place after the events of Galaxy in Flames and that Terra is already aware of Horus' treachery. However, both False Gods and A Thousand Sons (both written by Mc Neil!) explicitly say this happened before the Istvaan III massacre.
Also, The Flight of the Eisenstein states that Saul Tarvitz was the First Captain of the Emperor's Children and that Garro could see the oceans of Terra from space. Previous books had established that Tarvitz was never one of Fulgrim's chosen elite, and that those oceans had long since been boiled away in nuclear war.
Cool Sword - Many. The one from Laeran: with a Daemon in it, natch.
The Kinebrach's Anathame, which was a recurring plot device.
For the more mundane types, Thiel's Electro-magnetic longsword. Capable of shearing Word Bearer in two, cutting through star ship hulls and killing daemons more effectively than any ranged weapon
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 conflict 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.
Kasper Hawser has a twelve minute conversation with Longfang, in his mind, after the latter's death.
Death from Above - Long a favored trope of 40k, but it especially prevalent in Know No Fear. As a result of the Campanile hitting the Calth Veridian Yard causes the Andromacis to crashes into Kalkas Forticle. Then it goes to its logical extreme when an orbital depot is destroyed and parked vehicles start falling out into atmosphere—and right above the Ultramarines 6th Company.
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 Sigillite 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.
Space Wolves have a tradition of honoring those who died by passing down oral stories of warriors' lives. Well respected warriors receive a big "sending" or feast, in which a skjald or a good storyteller recites all the deeds of the fallen warrior.
Even Evil Has Standards - The Traitors Legions may have broken their oaths to the Emperor, but they still have standards.
In Nemesis Horus Lupercal forbids Erebus from employing any further assassins against the Emperor, as he considers assassins tools of cowards and the Heresy must end with Horus killing the Emperor.
When the Night Lords discover that the extent of the Word Bearers corruption goes to making several of their members hosts to daemons, they refuse to let the Word Bearers anywhere near them.
In Angel Exterminatus when the Iron Warriors realise just how depraved and insane the Emperor's Children have become they're not just unnerved, they're outright disgusted.
And then they find out what Fabius Bile has been up to in his spare time. Even people who spent their last pre-Heresy engagement committing genocide on their home planet consider Bile's horrific surgeries on Space Marines to be over the line.
Surprisingly, the Emperor's Children still have some standards when Lucius tells them that Fulgrim has been possessed by a daemon, and they resolve to free their Primarch. Granted, it was partly because they wanted to enjoy the sensation of fighting a Primarch, but it's pretty clear that Lucius, Mairus Vairosean, Julius Kaeseron, and Fabius Bile are motivated out of genuine loyalty to Fulgrim.
The barely-seen Brotherhood (normal humans in STC versions of Astartes equipment defending a peaceful non-Imperial system) in False Gods to the Astartes in general. Or maybe the Astartes to the Brotherhood.
The Space Wolves have the World Eaters as an evil counterpart, though their nemeses are the the Thousand Sons, who are completely opposite.
During the Great Crusade, Horus and Sanguinius were closer than any other Primarch. Anyone familiar with 40K's backstory is well aware of how that turns out.
Fulgrim and Ferrus Manus are said to be two of the closest Primarchs - They use weapons they forged for each other, and they both seek perfection, in their own way. When Ferrus refuses to turn traitor when Fulgrim reveals his treachery, it turns into a fight. When the Heresy begins, Ferrus becomes the first Primarch killed, and Fulgrim is holding the sword that did it.
Evil Weapon - Damn it, Fulgrim, a talking sword is not a good thing. Ask Elric of Melniboné.
Fake Out Opening - The first line of the first book is, I was there, the day Horus slew the Emperor..
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 similar to the Tau 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).
Because of the Edict of Nikaea, every loyalist Librarian (psychic Space Marine) is supposed to be this. Since some of Horus's worst weapons are psychic in nature, it's a nasty self-inflicted wound for the Imperium.
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.
Flashback to Catchphrase: The series shows some of several iconic phrases of the 41st millennium being spoken for the first time:
In Galaxy in Flames, Horus orders the Vengeful Spirit to open fire on Isstvaan III to start the firestorm phase of the virus bombing with the words that started the Horus Heresy, and which Abaddon would use to start the Black Crusades: "Let the galaxy burn!"
In The First Heretic First Captain Sevetar of the Night Lords become the first to utter the phrase "Death to the False Emperor!", a Battlecry that followers of Chaos have been using for ten thousand years.
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 characterization of those characters who had previously been relatively one-dimensional villains.
The whole of the Horus Heresy itself. We all know how this ends.
Foreshadowing: Starts as early as the first chapter of Horus Rising, where a Terminator Squad in the Luna Wolves is described as wearing black armor. Even more so because these particular Terminators are part of the First Company, commanded by none other than Abaddon. Yes. That Abaddon.
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.
Genuine Human Hide - We are contractually obligated to remind you that Chief Apothecary Fabius of the Emperor's Children has in his possession a lab coat made of human skin. It makes its first appearance in The Reflection Crack'd, where it's revealed to be from the skin of loyalist Legionaries slain during the Drop Site Massacre.
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.
In Fear to Tread the plan to turn the Blood Angels to the side of chaos by unleashing the Red Thirst in the middle of a battle with Chaos daemons ends with the Blood Angels unleashing a Curb-Stomp Battle on the daemons and giving Sanguinius time to recover from a Mind Rape and kill the Bloodthirster and Keeper of Secrets leading the daemons. Well thought out plan all round.
Heroic BSOD: The Traitor Legions actually have this as part of their strategy, knowing that the shock of betrayal will leave the loyalists at less than 100%. It works spectacularly with a lot of rank and file Astartes and more than a few Captains. The Primarchs on the other hand...not so much.
Hero Killer - The Space Wolves are this as the Emperor's weapon of last resort: a Legion designed to kill another Legion. It's been strongly implied that they were responsible for the "erasure" of the II and XI Legiones Astartes from Imperial history, and why the Emperor selected them to take Magnus the Red into custody for breaking the Edict of Nikea. When Horus changed the order from "arrest" to "kill", the Wolves didn't question the change in orders because it's what they were made for. And they would do it all again without a moment's hesitation.
Kasper Hawser: The unprecedented. Like... Astartes fighting Astartes? Like the Rout being called to sanction another legion?
Leman Russ: That? Hjolda, no. That's not unprecedented.
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.
The Vlka Fenryka, whose reputation is so bad that anything short of total guaranteed extermination is considered insufficiently risky to call them in - and sometimes not even that.
Hawser: The...the Vlka Fenryka are capable of Cannibalism? Skarssi: We are capable of anything. That is the point of us.
I Am Spartacus - All the Alpha Legion are Alpharius. It makes the scheming and unconventional warfare easier when the non-Legion don't know who's who. Taken Up to Eleven by the fact that not even the Alpha Legionaries are aware who's Alpharius at times besides Alpharius.
I Know Your True Name - Do you remember how in 40K knowing a Daemon's true name can give you power over the Daemon? It turns out the reverse also is true for the Daemons. Prospero Burns has A Tzeentchian daemon tearing through Space Wolves left and right because it knows their true names from Kasper Hawser. The only ones who are immune are Hawser, because he's an orphan discovered as a child who didn't know his own name, and Bjorn, who Hawser misinterpreted "Bear".
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.
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.
Life or Limb Decision - Kapser Hawser is forced to cut off Bear's arm to save him from the daemon's magic fire.
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.
Meat Puppet - Amon Tauromachian was controlled by a daemon who claimed to be Amon of the Fifteenth Astartes, Captain of the Ninth Fellowship in Prospero Burns. He couldn't move and he was forced to speak the words put into his mouth. Supposedly, he was controlled so thoroughly because Puppeteer had the same name as him.
Also, Kasper Hawser. Everything he saw and experienced was relayed to the daemon. His actions and memories were also subtly influenced.
More than Mind Control - Kasper Hawser's life was subtly influenced by a Chaos daemon instead of the Thousand Sons like was first though. The daemon could see and experience everything he did and influence his actions and memories.
Motive Decay - Horus suffers a bad case of "This is your motive on Chaos".
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 psychic 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. Although (presumably) in between these two stories he's seen as back to being rational in The Butcher's Nails, so it's anyone's guess how stable he is at any time.
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. Kharn'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.
To be honest, the Emperor had only ordered Leman Russ to apprehend Magnus and the Thousand Sons. The reason why the Space Wolves fought the Thousand Sons was because Horus (already worshipping Chaos, but still "loyal" to the emperor) told Russ that the orders had changed from apprehend to kill. Ironically, in the exact same situation, Magnus also broke it, since his warning obliterated The Emperor's work to open a gateway into the Webway, which would have allowed humanity to never have to use the Warp again. And for that matter, it's heavily implied that it was Magnus's earlier pact with Tzeentch to save his Legion that was the deciding factor in the Emperor outlawing psykers.
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.
In Angel Exterminatus, we find out the Emperor giving Perturabo some very specific advice. Rather then helping Perturabo avoid a mistake the Emperor almost certainly had foreseen, it ends up pushing him into Horus's camp after making the mistake.
Perturabo was also more than a little annoyed that an arena he built for contests of strength and skill was used solely to humiliate Magnus, one of the few Primarchs he got along with. By direct order of the Emperor.
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.
Noble Demon- Perturabo has shades of this. During the events of Angel Exterminatus its stated that he does not hate the Loyalist Legions, just sees them as being used and abused by the Emperor as much as the Traitor Legions were. He also allows the crew of the Sisypheum to escape after they destroy Fulgrim`s flagship.
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. The book also showed that Magnus the Red was quite happily able to go toe to toe with enemy titans when he wanted to.
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. This is repeated later on in Raven's Flight when he takes on an armoured division of Iron Warriors and manages to kill most of them before what's left of his legion becomes involved. Notably he effectively beats a Predator tank to death with his fists then uses what's left of it to kill an enemy tactical squad.
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.
Lion El'Jonson in Descent of Angels: He battles dozens of xenos which are actually daemons on Sarosh by himself without breaking a stride. Then in The Lion short story, he fights his way through dozens of daemons and concludes the incursion by stabbing Kairos Fateweaver, the most powerful Lord of Change in existence, in the heart.
Fulgrim in Fulgrim: He manages to cut through the Laer so fast that his own Terminator First Company cannot keep up with his kills. In the same novel, Ferrus Manus manages to cut through the Diasporex soldiers and get to their captain before Fulgrim can.
During the battle of Prospero Magnus uses his sorcery to inflict horrific deaths on hundreds of rock-hard Space Wolves. Then he uses them on Russ, which only makes Russ angry.
You'd be angry too if a gigantic Cyclops broke your armor to pieces with cold fire, punched his fist through one of your hearts, stabbed a psychic blade through your chest and out your back, killed the wolves that you likely grew up with, and were blinded by a painful ray of black light. Magnus didn't go down like a chump against Leman Russ, that's for sure.
Sanguinius finally gets unleashed in Fear To Tread: He takes out two Greater Daemons of Chaos within moments of each other: Ka'Bandha, a Bloodthirster of Khorne, by tearing off one of his wings and throwing him back into a Warp portal, and Kyriss, a Keeper of Secrets of Slaanesh, by cutting off his/her head.
Perturabo does this several times in Angel Exterminatus. Every time he picks his hammer up, everyone in his general vicinity dies very, very quickly. He is considered such a threat that the crew of the Sisypheum were willing to self-destruct their ship if it would take him out as well.
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.
Outgrown Such Silly Superstitions - "The Imperial Truth". Which would be great, if those pesky daemons didn't keep popping up. Not that the Emperor doesn't have a really good reason to try and quash knowledge of Chaos. 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.
The Paragon Always Rebels - Obviously. Ironically, Horus reveals that he thinks The Paragon is really Sanguinius. Erebus opines that it's Guilliman, predicting he would be the one to take over if something happened to the Emperor. He's right.
It's also why Horus tells Ka'Bandha to kill Sanguinius in Fear To Tread, both because Horus knew, deep down, that the Chaos Gods couldn't corrupt Sanguinius, and also because turning Sanguinius would result in a possible rival to Horus's leadership of the Traitor Legions.
Parental Favoritism - The Primarchs all have their rivalries, their favourites, and the Emperor does as well.
Pay Evil unto Evil - Multiple times the Horus Heresy paints the Emperor as, bluntly, an arrogant prick who held a great deal of responsibility for his sons falling and the heresy occurring in the first place. He waits a century before censuring Lorgar for establishing the Imperial Cult on conquered worlds, while simultaneously humiliating the Primarch and the entire Legion and destroying the innocent inhabitants of a world to make a point. He refuses to explain to Horus why he is leaving the Great Crusade, despite their closeness and the obvious damage the lack of trust did to his most favoured son. Magnus the Red arguably fared worst of all, as the Emperor specifically sends Russ and the Space Wolves, a Primarch and Legion who loathe Magnus and the Thousand Sons to their core to bring Magnus back to Terra, making it almost child's play for Horus to change the order to one of extermination
People Puppets - The daemon controls people with their names in Prospero Burns.
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.
In The First Heretic temporally displaced Word Bearers witnessing the creation of the primarchs contemplate pre-emptively killing the XI primarch to avoid the (implied) bloodshed that will happen when the legion is purged.
Hastur Sejanus also has strong elements of this in Horus Rising and False Gods.
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, and Rogal Dorn's Templars... 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.
Calth, in Know No Fear, is technically a victory for the Ultramarines, in that they still exist, but they had to really bleed for it.
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.
Recurring Dream - Kasper Hawser has several over the course of Prospero Burns.
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.
Subverted with Sigismund in Mechanicum. While he really, really wants to lead the Imperial Fists on a revenge spree against the Dark Mechanicum and kill everything standing between him and Kelbor-Hal, Sigismund ultimately realizes that Rogal Dorn's orders to secure Space Marine arms and armor from Mars is more important. But he's really displeased about it.
Played straight with Roboute Guilliman in Know No Fear. When learns that Lorgar deliberately orchestrated the Campanile crash, Guilliman informs his subordinates that the Macragge's Honour is going straight for the Fidelitas Lex. When he's called on it, Guilliman tells Gage that he knows that it's tactically dangerous to try and board the enemy's flagship this early, he just doesn't care.
Roaring Rampage of Revenge: Corax in The First Heretic. His Legionaries being cut down by the thousands, he tears through dozens of daemon possessed Word Bearers like a hot knife through butter, and would have killed Lorgar if not for Konrad Curze.
Roboute Guilliman in Know No Fear. The stoic master of warfare as a science goes absolutely insane on Word Bearers trying to board his flagship, beating them to death with nothing but his Power Fists. While on the hull of the ship without wearing a helmet.
Actually, the text seems to imply that he went to town on the Word Bearers without the Gauntlets of Ultramar, using only his normal gauntlets. Which is even better.
Sanguinius in Fear To Tread. With Ka'Bandha and Kyriss responsible for the deaths of hundreds of his sons, he throws Ka'Bandha through a warp portal and decapitates Kyriss, both of them with ease.
Serial Escalation — It's Warhammer 40000, which has been using this for decades, so it's only natural it starts happening. Specifically, this is the pre-heresy hat of the World Eaters Legion: to be willing to go one step further than the enemy will go.
Serrated Blade of Pain — The signature weapon of the Blood Angels Fifth Company are serrated combat knives used for flaying. They end up being the first Space Marines of the Flesh Tearers chapter.
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 Unorthodox 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.
The Strategist - Besides the Primarchs being peerless generals, this is part of the hat of the Ultramarines Legion: go into every battle with a theoretical (a sound understanding of what the situation is) and a practical (a solid plan of attack).
Stuff Blowing Up: All over the place - this is Warhammer 40,000 after all - but special mention goes to Know No Fear. The initial phase of the Battle of Calth has Dan Abnett channeling Michael Bay, with a commandeered ship utterly destroying Calth's space dock, a twelve-kilometer grand cruiser crashing into a city and demolishing it, and the destruction of a low-orbit depot causing a group of Ultramarines to experience a rain of main battle tanks.It's all described in loving detail, and it is awesome.
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.
Teeth-Clenched Teamwork - Sometimes, it seems like the only thing keeping the Traitor Legions together is the Primarchs. And even then, it seems like the only thing keeping the Traitor Primarchs together is Horus. Corax forms part of his strategy around it, believing that if the Raven Guard attack behind enemies lines and slow the Traitors advance, they can delay the inevitable attack on Terra, causing cracks to form between the Traitor Legions and they'll turn on each other. It does happen, just after the Siege of Terra.
The Star Scream: Age of Darkness reveals that Guilliman is training his forces to fight all legions, both loyal and traitor, and is formulating some sort of plan known as "Imperium Secundus". Whether this is to preserve something of the Emperor's dream or replace the Emperor is up for debate, as we still don't know what Guilliman's ultimate intentions are.
As of The Primarchs, Omegon is plotting behind Alpharius's back.
Took a Level in Jerkass: While generally considered a moral paragon by the standards of Warhammer 40000, 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.
Übermensch - 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.
Angron is also unpopular among his brothers, although Fanon has it that Perturabo and Angron are in some weird Buddy Picture relationship.
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.
Unstoppable Rage: The Blood Angels go into the Red Thirst en mass when Ka'Bandha kills five hundred legionaries and the psychic backlash sends Sanguinius into a coma. Unfortunately, it works too well, to the point that Daemons of Khorne are unable to fight off the Blood Angels.
Unusually Uninteresting Sight - In Know No Fear, Captain Ventanus notes that Sergeant Anchise's efforts to rally and redirect the remnants of the Ultramarines' 111th and 112th companies would normally become the stuff of legend. On Calth, it's simply another man's struggle before his death. Becomes much more interesting when those two companies become the backbone of the group that ends up reinforcing Ventanus in the end of the book.
Kyriss goes absolutely insane when Meros takes the ragefire into himself so that Sanguinius doesn't. He (she?) begins screaming in tongues and begins shouting that the Blood Angels are merely pieces on the board with no right to rebel. Sanguinius ends up decapitating it in the midst of its breakdown.
After spending the entire series as the most calm, collected, and unemotional of Chessmasters, Erebus goes off his rocker and verbally rips into Horus for interfering with the trap for the Blood Angels and courting the displeasure of the Chaos Gods, only realizing his mistake after he had let loose verbally on the Warmaster. Horus's response is actually pretty tame for a Chaos corrupted Primarch: he skins Erebus's face off, and reminds him that he is commanding the rebellion, not the Chaos Gods.
Betrayer revelas that Erebus's breakdown started even earlier. After screwing up the attack on Calth (earning a mocking dismissal by Lorgar) Erebus gets back up to his old manipulations again. His ego as "Destiny's Hand" is shattered when Lorgar tells Kharn (of the Betrayer fame) that Erebus was responsible for murdering his best friend. Kharn then utterly curbstomps Erebus to the point of almost killing him. Erebus cannot actually mentally comprehend that this is happening to him.
Ingethel has one in Aurelian during Logar's trip into the Eye of Terror when Khorne decides to test Logar in hand-to-hand combat with a Bloodthirster. To give an example of how bad this is, Ingethel, who is a Daemon Princess, is reduced to a sobbing wreck, repeatedly saying "Kharnath has violated the accord, Kharnath has violated the accord".
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.
A Wizard Did It - An in universe example, in Prospero Burns. Kasper's mind is altered by an alien force. When a Rune Priest enters his mind and finds details of Horus' betrayal, Leman Russ assumes that the prophecy was just implanted by the Thousand Sons as a ploy. Though he doesn't understand how that would work.
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. Surprisingly, Perturabo has a solid grounding in Olympian classical myth and is capable of incredible feats of civilian architecture such as theatres and arenas.
Woobie, Destroyer of 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
World With A Dark Secret: The Emperor locked the Void Dragon on Mars sometime in the 10th or 11th century (of the second millennium) because he knew that technologically inclined humans would one day settle it, and proximity to the Dragon would inspire them to design things for humanity's betterment.
Worth It - The Butcher's Nails leave those who suffer them mentally unstable, twitching unable to properly sleep. However, it gives Angron a type of serenity that he values.
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. Subverted most commonly by the World Eater/War Hounds Legion; Angron is depicted pretty consistently as rather undiscriminating when choosing targets.