* AlternativeCharacterInterpretation: The Horus Heresy novels tweak a lot of the various background details from the tabletop.
** Magnus the Red is known in the game as being a cyclops; in addition to his mighty psychic powers, his mutated genome caused him to only bear one eye, which was part of the reason why he was accepted by the planet of peaceful mutants he was "born" on. In Horus Heresy, he isn't mutated at all, he's just lost an eye.
*** Lampshaded in ''Betrayer'' - Magnus meets with Lorgar via astral projection right as the World Eaters and Word Bearers begin their assault on a particular world, and Lorgar notes how Magnus's face shifts between three forms: one where he simply lost an eye and the empty socket is sewn shut, another with one large, cyclopean eye, and another with just smooth skin where the other eye should be, as if the eye never existed. [[ContinuitySnarl These are all representations that Magnus has been given in fluff over time.]]
** The Emperor is portrayed as either a [[TooDumbToLive moron]] or extreme {{Jerkass}} (or a bit of both) who basically directly influenced the Traitor Legions to turn against him for understandable reasons.
*** [[AlternativeCharacterInterpretation Or]] a man with too little time, who had to either choose to coddle his adult long lost children or hope they were mature enough to deal with real life without daddy holding their hand?
*** FridgeLogic presents an obvious third interpretation: the Emperor is [[EldritchAbomination immortal and essentially unkillable]], so most likely he sees no need for sons or heirs at all. The legions and primarchs ''think'' he regards the primarchs in the way that a man might view his offspring because it's part of their brainwashing, but it's not actually the case: they are intended as simple tools to allow him to project his power in various ways, and he views their status as thinking beings as an unfortunate side effect. It never occurs to him that they might be 'offended' by only receiving the minimum information to complete the immediate task at hand because he doesn't actually think of them as people so much as a set of really fancy telecommunications gear.
*** Ultimately, the Emperor suffers from a truly awful case of DependingOnTheWriter. Creator/GrahamMcNeill generally portrays him as competent and benevolent (if flawed), Dan Abnett portrays him as competent but bloodthirsty, while Aaron Dembski-Bowden portrays him as a vicious, needlessly cruel imbecile.
*** Partly this seems intentional: that the Emperor and his actions are open to different viewpoints and interpretations. The traitors might argue he's lied and deceived them and the rest of humanity for his own power, and is no better than the tyrants many of them overthrew growing up. The loyalists in turn may argue that he had good reasons for concealing things from them, and even if they disagree with it Horus is wrong to take it to this extreme just because he feels hurt. It shifts the Heresy from less of a sudden betrayal by moustache-twirling villains to a more genuine civil war between different factions with their own arguments (as much as it can while still staying true to the core background story already set in place).
** The Literature/{{Space Wol|f}}ves are regarded as savage, brutish, even unworthy of being {{Space Marine}}s by their fellows -- in the 41st millennium, they are actually one of the nicer chapters.
** [[spoiler: ''Wolf King'' story reveals that though Leman Russ took his father's order to become TheDreaded and HeroKiller to heart, after destruction of Prospero and Magnus's presumed death he decided to abandon this role and change his Legion and himself lest they have no allies. It seems it worked.]]
** The Word Bearers, in "The First Heretic", are revealed to have a "quirk" in their gene-seed that induces extremely strong loyalty in them. Several of the characters who are aware of this openly worry about how much of their deep bond to Lorgar is natural and how much is influenced by this gene-flaw that fills them with an intense need for someone/thing to have faith in.
** The nature of the Second and Eleventh Primarchs and their so-called Lost Legions is left mysterious in the game in order to encourage players to create their own SpaceMarine chapters. In the Horus Heresy novels, it's stated several times that these two Primarchs and their Legions were wiped out and [[UnPerson Un-Personed]] ''by'' the Emperor and his other Legions for something, well before Horus was corrupted by Chaos. The precise cause is still a mystery, though.
*** That said, there are hints of them having turned against the Emperor in some fashion in the first novel. In ''Fear To Tread'', Sanguinus angrily refuses to admit the existence of the Red Thirst to the Emperor, declaring he will not have the only legacy of his Legion be a "third empty plinth beneath the roof of the Hegemon", implying that genetic flaws or deviances may have been the cause behind their destruction.
** In "The First Heretic", a daemon allows some emissaries from the Word Bearers to see through time and behold the embryonic Primarchs just before they are scattered across the galaxy. Not only does it claim that the Emperor actually bartered with Chaos to acquire the knowledge he needed to make the Primarchs and then sought to cheat them, it is actually direct influence from these time-traveling Space Marines that causes them to be scattered. Horus gets to do the same vision in ''False Gods''. It is unknown which group actually scattered them (both seem to have done the deed), though whether they're the actual ones to do it, or if that's just what they're led to believe, is up to debate.
** In a recent interview, Creator/DanAbnett says they often have to chose between conflicting versions of the same tale when they write it up for inclusion in this series, and that they think of these books as what actually happened, and the versions of the tales we know from earlier works being the versions as filtered through 10,000 years of oral history repetition between the Heresy and TabletopGame/{{Warhammer 40000}} proper.
** The Last Church, which takes place during the Age of Strife, heavily implies Terra wasn't as bad as the Emperor makes it out to be as most of the world's nations exist and peaceful travel can take place between them.
* ArchivePanic: Well... so far, thirty novels and stand-alone novellas, nine anthologies, twenty one audiodramas and one comic. Before you finish your ArchiveBinge, four to five more books are likely to be published. However, some people, rather than read everything, simply choose to follow storylines that interest them and read up on the rest online.
* SugarWiki/AwesomeArt: Some of the wraparound covers are impossibly amazing, such as the one for ''[[http://www.blacklibrary.com/Images/BL/blog/2011/07/Know_No_Fear_huge.jpg Know No Fear]]'' or, more recently, ''[[http://vignette2.wikia.nocookie.net/warhammer40k/images/a/aa/HHXXXI-Deathfire.jpg/revision/latest?cb=20150802102613 Deathfire]]''.
* BrokenBase: While UnpleasableFanbase is pretty much a constant for this franchise, some issues are more divisive than others.
** Imperium Secundus is redundant, brings nothing but padding to the plot and should have never been invented vs. Imperium Secundus is the only logical thing to happen and a fascinating sub-plot vs. Imperium Secundus has some nice concepts, but is overally [[TheyWastedAPerfectlyGoodPlot severely underused]].
** The franchise itself is either continuously interesting and pushes its plot forward at a good pace or it's getting steadily worse and has abandoned all pretense of advancing the plot in favour of turning into a shameless money-grab.
** New and revamped Ollanius Pius is either awesome or a fail on Games Workshop's part.
** The Emperor of Mankind is a brilliant genius who was forced to do some terrible things for the good of humanity vs. the Emperor is a whiny, self-absorbed warlord with delusions of infallibility. There's also the moderate part which believes that the Emperor is a good-intentioned, but deeply flawed being, and the people who theorize that [[TakeAThirdOption the Emperor of Mankind is actually not an ancient magical being, but an artificial human in the vein of the Primarchs created by Malcador, the]] ''{{t|akeAThirdOption}}rue'' [[TakeAThirdOption immortal protector of humanity, only a few hundred years back]].
** The Primarchs. ''Ye gods of Chaos'', the Primarchs. Lines are drawn in case of almost every single one and the debates that can break out could power Khorne for decades to come. Pretty much the only Primarch whom everyone can agree is generally okay is Ferrus Manus, and that's probably only because he died to early to become divisive. For the most heated arguments:
*** Roboute Guilliman is the most humane, easy-to-emphasize-with Primarch who has to make do with what he has vs. Guilliman's a {{jerkass}} and traitor to the Imperium.
*** Leman Russ is ObfuscatingStupidity and awesome vs. Leman Russ is a hypocrite of highest order and [[TheyWastedAPerfectlyGoodCharacter fails to deliver on his promise]]. The only thing the two sides can agree on is that he should be used more by the story.
*** Horus is a brilliant man who was tragically corrupted into serving Chaos vs. Horus couldn't stub his toe without coming to cry to daddy about it and it's no surprise that when the Emperor left, he threw a hissing fit.
*** Sanguinus is the most loyal son of pure heart and mind vs. Sanguinus is a traitor who considered cooperating with xenos and nearly sold his soul to Chaos. Not to mention the division of "if he told his father about the flaw, it could've been solved" vs. "if he told his father about the flaw, the Blood Angels would be purged".
*** Angron and Lorgar are tragic figures who had no choice but to turn against their father vs. they're narcissts who should man up and solve their problems by themselves rather than blame it all on the Emperor.
*** Perturabo is a NobleDemon and OnlySaneMan of the traitor Primarch vs. Perturabo is petulant and too preoccupied with his own misery to try and find some common ground with others.
*** Konrad Curze is a cursed figure of tragedy tortured by his own mind, whom we should pity vs. Curze is too edgy and too far gone and should be executed like a rabid dog.
*** Rogal Dorn is either a stalwart ReasonableAuthorityFigure or too hard-headed and inflexible to be fit for command.
*** Magnus was wrongly punished and did nothing wrong vs. Magnus should know better than to do what he did and now reaps what he sow.
** You're either with Perturabo and against Dorn or with Dorn and against Perturabo. No middle ground. Ditto for Leman Russ vs. Magnus. If you support one, the other side will rip you to shreds.
** Nykona Sharrowkyn is either cool or a MarySue.
** On a more meta level, among the series' [[DependingOnTheWriter various writers]], Aaron Dembski-Bowden can be considered a source of this, as he while overall considered a good writer, his interpretation of the Emperor as more or less a monster in ''The First Heretic'' and ''The Master of Mankind'' is not popular with most of the fandom and does not line up well with pretty much every other interpretation of him in the franchise, and is as such either [[FanonDiscontinuity ignored]] or considered to be from the perspective of his [[UnreliableNarrator enemies, and as such, not to be trusted]].
* ComeForTheXStayForTheY: Come for the backstory of ''TabletopGames/{{Warhammer 40000}}'', stay for the sheer amounts of badassery involved in some books.
** ''Know No Fear'': Come for Ultramarines, stay for the SceneryGorn as Abnett channels his inner Creator/MichaelBay.
*** Come for Roboute Guilliman punching a Space Marine's head off, stay for Oll Persson being BadassNormal.
*** Or, alternatively, come because you've heard that's the book where they bring Ollianus Pius back, stay because Guilliman is [[RescuedFromTheScrappyHeap actually pretty awesome]].
*** Come for the Ultramarines, stay for Aeonid Thiel, the first of their kind to study how to kill Astartes.
** ''Fear To Tread'': Come for Sanguinus and his Blood Angels, stay for Sanguinus/Horus {{bromance}}.
** ''Age of Darkness'' anthology: Come for the HoYay in ''Reflection Crack'd'', stay for the MindScrew of ''The Serpent Beneath''.
** The opening trilogy: Come for Horus, stay for Gavriel Loken.
** ''First Heretic'': Come to see the first Legion to fall, stay for the deep characters.
%%If someone wants to add Complete Monster back, actually provide concrete examples to avoid misuse. General statements just encourage misuse.
* CreatorsPet: Every single faction, literally. Most of the books are written by the Black Library author who wrote for the faction being explored, which results in said faction being unstoppably awesome and the strengths of the opposing faction barely receiving lip-service as they get slaughtered. ''Betrayer'' is perhaps the worst case of this, narrowly edging out ''Battle for the Abyss'' (in which about a dozen Loyalist marines destroy one of the largest ships in the galaxy, stuffed to the gills with Word Bearers).
* EnsembleDarkhorse:
** Garviel Loken is the prime example, starting out simply as POV of the first trilogy and getting so much fan love, he was one of the first characters introduced to the tabletop game of Heresy.
** Tarik Torgaddon and [[OnlySaneMan Hastur]] [[WhiteSheep Sejanus]] have a large following, the latter more puzzling because for 99% of the series, he's TheGhost.
** Sigismund is almost universally beloved by fandom, although there are two groups of fans. One, prowling the forums, loves him for his sheer fighting prowess and awesome he brings wherever he goes, while the other, residing mostly on Website/ArchiveOfOurOwn and Tumblr, loves exploring his tragic relationship with his gene-sire following ''The Crimson Fist'' and revelations thereof.
* DesignatedHero: Even before the actual heresy and before any Space Marine had fallen to Chaos, many of the actions undertaken by the primarchs and the expedition fleets were... questionable, at best. Fulgrim and Ferrus Manus's ruthless extermination of the Diasporex, a democratic confederacy where humans and aliens lived in peace together and only wanted to be left alone, simply because the humans co-operated with xenos and refused to join the Imperium, is probably the best example.
* HarsherInHindsight: To anyone familiar with 40K's lore, the entire first chapter of ''Horus Rising'' counts as this. References are made to the "impossibilities" of a civil war in the Imperium and Astartes fighting Astartes. Abaddon himself (who would become Abaddon the Despoiler, leader of the Black Legion, the remaining Chaos-aligned Luna Wolves) even addresses the ruler of the planet they're attacking (who calls himself the Emperor of Mankind) as a "False Emperor." It's enough to make you cringe.
** In ''False Gods'', Horus tells Maloghurst that "Ten thousand years from now, I want my name to be known across all the heavens," in the context of allowing a self-important remembrancer to become his biographer.
* HesJustHiding: Many people don't believe that the man [[spoiler:Dorn killed really was Alpharius]], and even those who do are convinced a resurrection scheme is already in place.
* HilariousInHindsight: That quote from the scholar Karkasy in the first Horus Heresy book: [[spoiler: "Most vigorous of all was the Imperial Creed that insisted humanity adopt the Emperor as a divine being. A God-Emperor of Mankind. The idea was ludicrous and, officially, heretical. The Emperor had always refused such adoration in the most stringent terms, denying his apotheosis. Some said it would only happen after his death, and as he was functionally immortal, that tended to cap the argument."]]
** Made even more hilarious when in ''Vow of Faith'' we find out that [[spoiler:Karkasy's now the greatest supporter and pretty much second-in-command to Euphrati Keeler, the chief preacher of the Imperial Creed.]]
** Aeonid Thie, an Ultramarine sergeant know for getting in trouble for using unorthodox tactics [[spoiler: Is the co-writer of the Codex]].
* HolyShitQuotient: Two situations in particular [[BrokeTheRatingScale break the rating scale]].
** The Battle of Istvaan V, also known as the Drop Site Massacre. Among its highlights, eleven Legions battling each other eight-against-three, Ferrus Manus getting killed in a duel against possessed!Fulgrim and Vulkan ''sending enemy heavy tanks flying with his hammer''.
** The opening of the Battle of Calth and the total, absolute massacre both in space and on land. ApocalypseWow indeed.
-->''It starts to rain main battle tanks.''
* IncestYayShipping: Like you wouldn't believe. With LoadsAndLoadsOfCharacters being mostly related to each other via genetic engineering, ship-oriented parts of fandom have largely ignored the implications and just sailed on.
** There are enough Primarch ships to form an entire battlefleet, with Horus/Sanguinus as the flagship. Almost every single combination has been explored online...
** Father/son ships also abound, mostly Curze/Sevatar and Dorn/Sigismund, the latter of which truly set sail after ''The Crimson Fist''.
** Let us also not forget of the One True Foursome that is Mournival.
* MagnificentBastard: Horus. Again.
** Lion El'Jonson loves his Xanatos gambits and secrets, but he is the primarch of the Dark Angels.
** Lorgar and his Legion tend to take the cake, given they set everything rolling.
** The [[spoiler:Alpha Legion operative]] in the Age of Darkness story 'Liar's Due' has this as his hat. He [[spoiler:manages to make a loyalist world self destruct/declare for Horus with a single broadcast and their own prejudices.]]
** The [[spoiler: demon in ''Prospero Burns''. It planted a spy in the Space Wolves that it knew the Wolves would find and believe was sent by the Thousand Sons, which in turn guaranteed that when Magnus the Red tried to warn the Emperor of Horus's impending betrayal via sorcery, he would not only be disbelieved, but treated as a traitor. As a direct result, the Space Wolves were all but annihilated the Thousand Sons and Magnus turned in desperation to Tzeentch to save what remained.]]
*** Not only that, but the above plan was considered only a ''partial victory''. [[spoiler:The demon (possibly Tzeentch/one of his agents) had intended for the Space Wolves/Russ and the Thousand Sons/Magnus to destroy one another completely, as they represented the most powerful magical and physical barriers (respectively) to Horus's impending heresy. Instead, the Space Wolves were only bloodied, but the Thousand Sons survived and turned to Chaos.]]
*** And now, as of Age of Darkness's last story, [[spoiler: it appears that Lion El'Johnson may not be as deceptive as first appears. That honour would go to... Roboute Guilliman.]]
** [[spoiler:Madail]] would qualify, too. For most of ''The Damnation of Pythos'', the Iron Hands might as well be renamed the Iron Marionettes for how well they got suckered by him.
* MoralEventHorizon: Pretty much what the series is about.
** Really, the whole thing is the MoralEventHorizon of the Chaos Gods. All the tragedy the galaxy suffers is ultimately due to them manipulating things for their benefit. Even with all the push the Emperor gave to the Traitor Legions, the Chaos Gods still spent years malevolently plotting to bring down the Imperium and drag mankind into darkness, especially with the corruption of the Sons of Horus, the Word Bearers, and the Emperor's Children. The destruction of Prospero in particular is tragic, which should come as no surprise as it was caused by Tzeentch, long considered to be the most malevolent of the Chaos Gods. The followers of Chaos itself may have become more sympathetic with the ''Horus Heresy'', but the Chaos Gods themselves have lost all claim of sympathy.
* {{Narm}}: Sometimes the authors try dramatic... and fail.
** "This. World. Is. ''MURDER''!" So much for using up those few seconds of free communications you've had...
** "Vulkan lives!" By the end of ''Deathfire'', you're going to wish he was actually perma-killed, if only for Salamanders to finally stop repeating this like parrots.
* OneSceneWonder: Uriah from ''The Last Church'' appears in a grand total of a single short story, but easily leaves a lasting impression. Quite possibly because he gives a TheReasonYouSuckSpeech to ''the Emperor''.
* RescuedFromTheScrappyHeap: After this infamous Ultramarines codex plunged them straight into MarySue territory, their Primarch Roboute Guilliman became fans' chief [[TheScrappy Scrappy]]. The books, however, with his commentary on how Codex Astartes is not a bible, his approach to the common man and general badassery (punching a man's head off, anyone?), combined the fact that he's the only Primarch to improve the lands he has conquered, did a lot to make him more likable in readers' eyes.
* WhatAnIdiot: The Emperor's entire approach to knowledge of Chaos, knowledge of his plans, and certain actions taken towards his sons which almost certainly contributed directly to their corruption and/or betrayal. For a being of such towering intellect, the Emperor seems to have made it his goal during his later life to take the IdiotBall and set a new scoring record.
** He was a being of impossible power. Almost divine in nature. As more divine a man becomes, just as well his humanity fades. It is not unfeasible to believe that he was disconnected from humanity in such a way that he did not expect certain things anymore, like his sons disloyalty.
*** The Priest in The Last Church realized this to be the Emperor's fatal flaw; that the Emperor simply could not comprehend lesser beings' (i.e. everyone else) need to believe in something greater than themselves, among other things.
** ''A Thousand Sons'' suggested that fearing daemons makes them more dangerous, that withholding information about Chaos might actually be a fairly effective strategy, but whether this is lost knowledge or more of Tzeentch's misinformation is never addressed.
*** The main issue being that, looking at the rest of the lore, it's not just fear. Depending on the demon, getting angry at it for eating your civilians, feeling friendly ambivalence toward it, or even actively denying its existence (as with the apocryphal chaos god of atheism) might empower it. People slavishly revering the emperor for his claim that he wasn't a god is heavily implied to be one of the things that amped him up to god level in the first place, and demons are even more efficient at harvesting that kind of power.
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