Known as the Legio Cataegis (Latin: Storm Legion), they were formed during the Age of Strife, when the Emperor judged that it was the right time to make His presence known. He needed some advantage over the warlords, techno-barbarians, and other would-be world rulers that were currently reenacting Mad Max all over Terra, and so He created twenty regiments consisting of hundreds of genetically enhanced soldiers, led by commanding officers known as "primarchs" (one of these primarchs was named Ushotan, and he was in command of the IV Legion, who specialized in siege warfare). These soldiers wore simple, smog producing, yet flamboyant and decorative powered armor. Because the Emperor's symbol at the time was a raptor and thunderbolt, this symbol was prominently displayed on the chestplate of the armor, the armor came to be known as Thunder Armor and the warriors who wore said armor were called Thunder Warriors in Low Gothic.
Created using a simplified cookie-cutter version of the Custodes' bio-alchemy on adult subjects (in contrast the Custodes' custom-tailored process subjected on infants), the Thunder Warriors were devastatingly effective and quickly became icons of the Emperor's armies; just the threat of the Thunder Warriors' arrival could convince a warlord to surrender, and those who refused quickly learned that the Thunder Warriors' reputation was not exaggerated. According to the fluff, they were even more physically powerful and ruthless than the Space Marines. And while physically stronger, they were not nearly as mentally or physiologically stable, and overall FAR inferior to the Custodes.
And yet, for all their successes, the Thunder Warriors were not perfect. Though at the time, it was believed they were, in fact, the pinnacle of mass produced military genetic engineering. However, along with Amar Astarte (the "mother" of the Thunder Warriors, Primarchs and Space Marines), the Emperor was able to refine the process and stabilize the genetic instability that ran amok in the Thunder Warriors, utilizing the Astartes Primarchs as templates to stabilise a new breed of warrior.
None of them could be counted on to last long, as either their minds or bodies gave out at unpredictable intervals, and the technology didn't yet exist to give them a lifespan longer than the average human's. They were suitable for fighting the barbarian human armies of the Age of Strife, but not for the long, star-spanning campaign of the Great Crusade that the Emperor had set as His next goal, so as soon as He had enough territory to set up a secure laboratory and enough scientists to man it, He set to work on the next generation of warriors: the Primarchs. Interesting to note, when confronted by Chaotic energy, whilst the Custodes were immune to Chaos, the Thunder Warriors seemed strengthened by it at the cost of mental control. During the war against the Confederacy of Maulland Sen (one of the earliest conquests in the Unification Wars), they were exposed to Warp energy, which drove them into a berserk frenzy and caused them to butcher everyone in their way, even noncombatants and those whom the Emperor would have preferred to keep alive. The amount of carnage from their exposure to sorcery was the first serious cause for concern in all Imperial chains of command.
This may indicate that the Thunder Warriors' augmentations involved Warpcraft. Which would make sense as Thunder Warriors and Astartes alike commonly demonstrate superhuman physical abilities far beyond any augmentation could hope to justify. Such as relatively unequipped Thunder Warriors slaughtering War Hounds with several Astartes killed for each Thunder Warrior dead even after many years of genetic degradation. Valdor even obliquely states in context with the Thunder Warriors that it was necessary to create subjects [The Primarchs] that were in greater control over their powers. So it's clear psychic mumbo jumbo is at work and that it was not working right with the Thunder Warriors. He also states that the project failed and [after the Scattering] only the smallest fragments remained - hinting that the Astartes and Thunder Warriors were supposed to be much more.
The Thunder Warriors were not what He envisioned as the defenders of humanity; they were blunt tools of destruction and little else. It is very important to note that the Astartes were already in circulation before the Thunder Warriors were "retired", the First Legion had already been established and Proto-Legions all the way up to the XVIIIth were seeing active combat. The Emperor saw no great loss in removing them for good now that they were obsolete. The Imperial records indicate that the last of the Thunder Warriors all perished at the Battle of Mount Ararat, which is strongly believed to be a cover story. Though the details are scarce, the battle did actually happen and there were survivors, hinting at a possible betrayal and a cull instigated by the Custodians.
However, contrary to this popular viewpoint, the retirement of the Thunder Warriors may not have been a betrayal and perhaps something less dickish; more like putting down an old guard dog with cancer than a complete betrayal. The Thunder Warriors leader: Arik Taranis is vague on the details and admits he holds no ill will towards the Emperor for what he did. Another survivor: Dahren Heruk still considers himself loyal to the Emperor and holds to his pre-Unity oaths. More interestingly, when Heruk rescues a Custodian from a group of Alpha Legion hiding on Terra, the surprised Custodian thanks him and seems prepared to leave him where he is, at least until a mortally wounded Heruk halts him to request and be granted an "honoured death" (basically a mercy kill with a blade through the heart). Like Arik and Ghota, Heruk's group of Thunder Warriors are all failing physically, filled with cancer, and required to undergo regular organ transplantation just to stay alive; and are failing mentally, wracked with hallucinations of the Unity Wars like soldiers with PTSD. It may be that the last of the Thunder Warriors went willingly to their ends at Mount Ararat at the very height of their eminence, knowing that they could go no further than that. The alternative being eventual madness and inevitable biological collapse, coupled with being rendered obsolete in the shadow of the newly rising Astartes. Heruk remembers the battle of Mount Ararat to have been glorious with little to no bitterness, and he and his companions all believe that they have simply lived too long.
The 8th Edition Custodes Codex explained that the Thunder Warriors were purged after they rebelled due to learning that they were engineered with intentionally short lifespans. More specifically, they revolted over what they perceived as the Emperor's betrayal for deliberately giving them a shortened lifespan. Ironically, the remaining Thunder Warriors were purged by the first few thousand prototype Astartes from the I Legion in their first combat engagement after joining forces with Imperial officials planning a coup. As such, it would make sense that any surviving Thunder Warriors would be those whose loyalty to the Emperor prevented them from holding such a grudge.
The so-called "cull" wasn't the end of the Thunder Warriors, though, as some of them managed to escape and spread throughout the Imperium. Per Horus Heresy Book Nine - Crusade, scattered bands of survivors endured in hiding through out Terra and the immediate space around the Sol System but most were systematically hunted down and liquidated by the I Legion. In one notable incident during the Great Crusade, there was an insurrection on the asteroid prison colony of Cerberus. Though the Thunder Warriors were not the only members of the rebellion, there were enough of them to form a group calling themselves the Dait'Tar. The Emperor did not like that and sent an army of War Hounds to crush the prison riot with impunity. The Astartes having gotten bored with maiming and killing prisoners not worthy of their challenge, found themselves some Thunder Warriors grouping up in a defensive position. Instead of just showering bullets on the surviving Warriors like a more sensible Legion might have, the War Hounds rushed in and engaged them in close combat. But Thunder Warriors are basically mini-Primarchs without the immortality, and were able to claim three to four Marine kills in melee for each Warrior that went down. After five hours of carnage and RAEG of old vs. new, the Imperial Army forces waiting in orbit got bored and decided to join the party, but the party was already done and left nothing but Thunder Warrior corpses, lots of War Hound corpses, and lots and lots of regular prisoner corpses cut down apparently trying to escape the melee.
Others descended into the Underworld of Terra, taking roles amongst the criminal element or eking out a living as gladiators. One group managed to steal an Astartes progenoid gland to extend their lifespans and went into hiding, so far not to be seen again.
It is generally accepted that peak Thunder Warriors probably (the fluff is hazy on this) fall somewhere between Astartes and Custodes on the scale of who-beats-who. Though their exact capabilities are not covered in any great detail. As a military force, the Thunder Warriors were considered unmatched even in their time, yet were recorded as being lacking in discipline. Custodes vs Thunder Warriors has gone both ways with both being said to be unmatched even though both existed concurrently. So it may simply be that Custodes utilize teamwork and Thunder Warriors do not or who knows what. Since Custodes are made using the Emperor's own blood, they likely more potent fuck-physics superhuman capabilities.
During the Unification Wars, every Warlord and his dog had access to some form of advanced technology, whether through cyber-augmentation, bio-alchemical processes or genetic tampering, the Thunder Warrior was supposed to be superior to all of them. In HH1 they were claimed to have "unprecedented superhuman physical power, gene-programmed resistance to environment" and most notably: resistance to "psychic attack". However, in the context of the statement the Thunder Warriors were explicitly superior to anything the Emperor's enemies could field against him rather than by him; however the HH7 entry for Custodians explicitly states that they were designed to be "stronger, faster, more acute of sense and more resilient than even the doomed Thunder Warriors", pretty much putting the matter to bed. Yet in their time the Thunder Warriors existed as a legion while there were only a handful of Custodians attending the Emperor, so they easily projected a far more dangerous military threat. Even by the final Battle of Ararat there were only a few hundred Custodes, so the Thunder Warriors remained the deadlier force while the Custodians were still some barely understood figures who remained at the Emperor's side and it took the new Astartes warriors to eventually take down the Thunder Warriors.
Resistance to psychic attack is particularly notable, since while his Custodians and Astartes are possessed of some impressive willpower and determination, as well as a lot of hypno-indoctrinated mental safeguards, they seem to be no more or less able to resist psykers than any other human. What's more is that we can possibly narrow this down even further and credit it to the Emperor directly, rather than any form of genetic/biological upgrade. Merir Astelan and the first 5000 Space Marines all had similar psychic wards build into their minds granted from the Emperor himself, manifesting as a golden aura that seems to make psychic compulsions have no affect on them, and giving telepaths headaches for trying to read them. This is probably why the later Astartes don't share this capability, as the Emperor probably didn't have the time to mind-lock every soldier under his command. Additionally, while they did not seem vulnerable to mutation or mind control upon being exposed to sorcery, the Battle of Maulland Sen demonstrated that Warp energy exposure made them go berserk in a manner that would make even pre-Heresy Angron surprised in his more lucid moments. This implies the Thunder Warriors' psychic resistance was actually part of their enhancements and not from the Emperor's personal attention. And "resistance" probably translated to "murderize everything in range until you kill the psyker".
In terms of tactics and physical combat, it was noted by observers that the Astartes and Cataegis were very different in combat style and doctrine during the Palace Coup's battle between Valdor's first batch of Dark Angels initiates against the Thunder Warrior Survivors and their allies. Whereas the Thunder Warriors and their Primarch, Ushotan, were described as flamboyant; emotionally unrestricted; and individually imposing, the first Dark Angels were described as functional; mechanical in nature; and methodical. Additionally, while the book, Valdor: Birth of the Imperium, made clear that each Thunder Warrior and Ushotan were individually larger and more powerful than each Dark Angel they fought, the latter were described as almost always wounding or maiming their Cataegis opponents before they died and were replaced by reinforcements that would eventually wear their opponents down. Whereas Ushotan was described as a single berserk bear (in contrast to the Thunder Warrior Dahren Heruk's description of the Custodes as an indomitable pride of lions), the Astartes were described as a pack of instinctively coordinated wolves that gave him significantly more trouble than the power armored techno-barbarians he typically mowed down with contempt. The fact that they were on the verge of overwhelming him made Constantin challenge Ushotan himself to give the Cataegis Primarch a more fitting and honorable death.
In any case, a few things are clear. While they do have additional organs (seeing as they had to harvest organs from their own dead rather than from normal humans to prolong their lives), there are a number of organs/abilities they do not have.
- No Black Carapace; the original Mk. 1 Thunder Armour was never designed to function with one, so Thunder Warriors wore their heavy armour like any mortal would, rather than interfacing with it like a second skin.
- They don't have a secondary heart, as seen with their tradition of "Honoured Deaths" with fellow warriors mercy killing mortally wounded comrades with a blade through the heart.
- They also don't have a Betcher's Gland; one of Dahren Heruk's companions, Vezula Vult, forgot about this when he tangled with a group of Alpha Legionnaires in the slums of Terra, getting sizzled in the face by acid because he wasn't paying attention and joked about how "He gave them all the gifts. Didn't He?"
- They may not have a Larramans Organ (or equivalent) as each of Heruk's companions were shown bleeding out at various points rather than have it clot in moments the same way that Astartes do: Kabe, after being stabbed with a spear was shown to have a pool of blood forming beneath him and was beyond saving by the time it was accumulating in his lungs; Gairok had blood bubbling from his lips after being run through with a sword; while Vult was also shown to be slowly dying from a wet and dark wound to the gut some time after the wound had been inflicted.
- Finally, and probably most importantly, they don't have a Progenoid Gland, which for Space Marine is the eau de Astartes, making them everything that they are and providing the means to make more of them.
These points aside, the fact the Thunder Warriors are physically superior to Astartes is not really in doubt, with each conflict in the fluff between them generally resulting in it taking several Astartes just to bring down a single Thunder Warrior, and even in most of these reported situations, the Thunder Warriors in question are long past their physical prime and are undoubtedly in the throes of genetic degredation, so who knows that they might have been capable of at the peak of their power. They might have been directly superior to Custodians, who knows? The best example thus far is the duel between Primarch Ushotan and Constantin Valdor; both the highest exemplars of their respective breeds. Though Ushotan was wounded by several Astartes he slew before the duel actually started, with both combatants having started the battle at the same time and Valdor had since gone through a number of Thunder Warriors singlehandedly so it's still a fair starting point. Ushotan still had the strength to check several of Valdor's blows which Valdor had to return by piling more strength upon strength (even in his superior auramite armour). However, Ushotan was tiring from lactic acid build-up, which Valdor exploited with a perfectly timed strike. The Thunder Warrior may have been stronger, but the Custodian fought with unmatched martial perfection and could perceive the flow of the fight even while it was happening and presumably didn't apply one hundred percent strength and was able to work his way up while his foe had to go one hundred percent and stay there trying to fight exhaustion as he had no other advantage.
All things considered: a Dreadnought is deadlier than a single Space Marine, but the Imperium does not force healthy Space Marines to become dreadnoughts simply because they are deadlier. An Ogryn might be capable of tearing a Marines arm off, while an Assassin might be swift enough to punch through power armour, but they are all reserved for specific situations and purposes. The same should be said between the differences between the three different branches of superhuman: The Custodians were intended to be peers and guardians of the Emperor himself; and remain with him in whatever future he had planned for humanity. The Astartes were designed for long campaigns that stretch out over centuries, and were capable of fighting in any number of environments against strange alien foes. In a similar way that a lance is better at stabbing than a shorter but more versatile sword, the Thunder Warriors were designed to fight in one environment against one set of foes from one planet: Terra. A single campaign against some of the deadliest examples humanity could throw back at them, so it is no wonder they seem to do so well compared against Space Marines and Custodians, since they are more a tool/weapon designed for only one circumstance.
"There was never time for perfection, and so the Cataegis were always a compromise. They were the best that could have been created under such conditions, but nobody believed they were permanent."
- – Amar Astarte
As to the issue of longevity, the Custodians and Astartes don't age (well, they get the cosmetics of aging but it's only skin-deep and in a sexy GILF way instead of spots and wrinkles). The Emperor could have granted the Thunder Warriors longer lifespans, even biological immortality (it's actually pretty simple since aging is caused by imperfect DNA caused by cellular division; make division create perfect copies and there is no aging), but what would be the point of extending their lifespan if he did not intend to make any more of them since they were only required to take over one world (and maybe in a best case scenario Mercury, Venus and the Moon to suicide against the biggest nasties present) anyway?
The Emperor had twenty more groups of transhumans ready to take over the known galaxy - the sheer number of worlds and the distances between them practically demands the creation of a military force that can stand the test of time. One could then propose that if the Thunder Warriors had longer lifespans then they could have fulfilled that role instead of the Astartes. But as mentioned above, while they might have been physically superior, they simply weren't equipped with the same augmentations that might be useful in more varied environments. Thunder Warriors were designed for a task and they performed it well, providing them with immortality to survive beyond this would have been needlessly sentimental.
It is also interesting that the issue of raising new Thunder Warrior regiments hasn't been brought up; The Thunder Warriors clearly had the medical knowledge to attempt to delay the failure of their physiologies, but either lacked the facilities or the desire to make more of themselves. Very little is known about Thunder Warrior recruitment and augmentation processes such as how long they take, what standards they must adhere to and what specialised equipment is required to create them. By contrast the Space Marines are equipped with their own means of reproduction; the Gene Seed allows them to make more of themselves from varied human sources (for example, the IXth Legion were even able to recruit from mutated stock) and without direct oversight even when on campaign far from their home-worlds. Even if the Thunder Warriors were superior combatants in every conceivable way, the ability to replicate virtually unlimited "lesser" superhumans anywhere in the galaxy is an advantage too great to give up.
The Emperor could have simply made custom augmentations for each Regiment/Legion of Thunder Warriors to specialize them for each intended purpose and could have used the knowledge from the Mechanicum and cybernetics to correct the genetic flaws and smooth things out. Considering that this was how he ended up with twenty Astartes Legions, then why not bring both programs together and create Thunder Warriors with added organs so they could adapt to different environments, or make Astartes with greater size, strength, and resilience on a par with the warriors that preceded them? Considering his development of Primarchs, Astartes, and Custodes, he clearly had enough knowledge, and skill, and tools to do this, whether it was cost effective or not is a different matter; as Constantin Valdor once mentioned that to make an army of Custodians on a similar scale to the Thunder Warriors would have practically bankrupted Terra, and who knows if the programs were even compatible with each other?
In any case: As much as people try to put the blame squarely at his feet for being lazy or short-sighted; Amar Astarte claimed that while his influence certainly sped things along, the Emperor was not the only person working on his transhuman projects. He had enormous laboratories with hundreds, if not thousands of scientists working in secrecy just to get as far as they did with the Space Marines, and had been working on the Space Marine project even before the Thunder Warriors exists, they were just a stop-gap. Bearing in mind that the project was set-back and all of the laboratories were destroyed twice. First with the Scattering of the Primarchs due to the fucking moron Erda dropping the anti Chaos God defenses to protect the Primarchs (which would severely backfire), secondly when Amar Astarte herself decided that the loss of said Primarchs was going to doom the Astartes Program to the same failures as the Thunder Warriors - a very telling reason indeed- This means the Great Crusade race was essentially started early, as the Emperor was now on a timer in order to reclaim them before they were irretrievable and still needed to build the Astronomican, claim Mars and get himself out into the galaxy to meet his sons.
The fact that Primaris Marines now exist that are larger, stronger, and more resilient than basic Space Marines shows that the gap has finally been filled. They are still not the equals of Custodians on the tabletop, but we're only talking the about the level of variance within a single point. They are probably much closer to Thunder Warriors and are potentially what the Emperor always intended, if he had the time to focus on his project and continue, or at the very least just one or two steps below, Thunder Warrior level fighters with all the stability and mass production capability of Astartes.
Considering the threats to Unity and dangers of Terra at the time; From nations of psykers to Men of Iron hidden within the core of the planet, and Chaos licking their lips the whole time, let alone everything else like the Rangda and Orks hitting critical mass and bulldozing everything. It's unsurprising the Emperor moved as quickly as he did and used every tool at his disposal.
Thunder Warriors seem to have been poorly armed compared to Custodes and Space Marines. While some assumed Volkite weapons, Plasma and Rad weapons would have been standard issue. This was not the case. They used larger versions of Bolters and Lasrifles. Yes the standard issue weapon of the Solar Auxilia. That's like making the standard issue weapon of the Custodes Hotshot Lasguns. Some also had what looked like Power Weapons or some equivalent. No wonder their shit was pushed in by Empys bodyguards and the Dark Angels. Their weapons were utter garbage compared to the stuff the new boys got. Good thing for them Terminator armor didn't (or shouldn't) exist at this time.(disclaimer because Black Library writers tend to forget their own fluff) The battle described in Valdor: Birth of the Imperium would have wound up even more one sided in favor of the fucking new guys.
They also employed Skylance, the predecessor of Stormbird. So one can guess they had decent air support at the very least.
The first badass granddaddy of all Space Marines and Thunder Warriors who would make Guilliman and Dante envious for his existence. He was known to win lots and lots of battles for the Emperor, survive dozens of suicidal fights in which countless Thunder Warriors (who are stronger than space marines) would die, especially the last battle in which he barely made it to victory with his comrade. The Emperor, knowing the Thunder Warrior's limited lifespan would not serve any good for his future conquest, decided to abandon the Thunder Warriors by arranging an utter betrayal with Arik that would make Horus look like a saint. As a result, Arik was forced witness the killing pretty much all his surviving comrades while according to the record, it would be reported that Arik and the Thunder Warriors had been honorably slain during the last battle. Despite the betrayal, Arik had no sense of hatred towards the Emperor, for he knew that Thunder Warriors would only serve as an impediment to their future cousins and he understood the stakes of the Great Crusade.
Anyway, Arik would later hide among Terra's population with his large, obvious body and become the Kingpin of Terra. He started out in the Petitioner's City of the Imperial Palace as the leader of some pissant gang named Dhakal, gang raping his way up the food chain with his only remaining Thunder Warrior buddy, Ghota (who, as described in The Outcast Dead, is an overgrown, cantankerous motherfucker with eyes like the rage zombies from 28 Days Later, apparently a side effect of the Thunder Warriors' painful physical degradation) and at least thirty other survivors, until he was effectively the big cheese of gangsters. Calling himself Babu Dhakal (or at least everyone else called him that... the man was crazy, but he wasn't crazy enough to address himself in the third person), Arik expanded his control until it encompassed Drugs, bitches, gambling, weapons, and even toilets--the absolute madman! He would go on to control criminals and heretics alike, causing the Adeptus Arbites to rage quit because they couldn't handle Arik's near swaglord level reputation and rampant (to the point of being fucking psycho) badassery.
He somehow got lucky and found a secret and surprisingly advance lab with all the necessary equipment buried within Terra which is about as common as finding a functional buried starship on a post-apocalyptic Terra. Meaning it probably wasn't an accident at all. This, coupled with the scientific knowledge he somehow got from the Emperor (which it is not explained whether Emperor "shared" it, Arik being a badass and learned it from just watching, or the Emperor directly taught him in order prepare for some kind of backup plan.) would help him to genetically modify and increase his life span (but not really enough to keep him alive -- until the Horus Heresy came around).
The Outcast Dead incident
When heresy first became a thing that happened in the Imperium, Arik managed to get a functioning Progenoid Gland from one of the outcast dead space marines (it's unclear which one, but they probably didn't mind too much--being outcast and dead and all). He was able to extract at least some of the information he needed to replicate the gland, and was then able to plant a functioning copy he had created within his own body, as well as Ghota's. Since GW never expanded their storyline, we can assume that either they have successfully outlived the Emperor and become more rapey, pillagey, and space piratey than the Dark Eldar, or that the result of all their careful work was that they up and turned into uber powerful heroes of the Imperium... we have no idea. They may have just settled down on Terra. However, since the Siege of Terra is getting its own series, it is possible for them to show up again.
Arik Taranis Facts
Despite being outdated and retired, Arik has demonstrated some epic Primarch-level shits:
- He knocked down the "Azurite Tower" during the Unification Wars, as well as earning tons of fucking countless titles.
- He survived the Battle of Mount Ararat, a final yet deadly battle that nearly wiped out his army, meaning he gets shit done even if it almost killed him.
- His Thunder Warrior subordinate Ghota can fight 5 elite Astartes to a stalemate even killing one of them, yet Ghota bows to Arik. Although that doesn't mean Arik is physically stronger than Ghota, is just Ghota having more loyalty to his master.
- Arik has the Emperor's knowledge on gene-seed which the Emperor somehow allows. If Arik were still be alive today, he could probably be the greatest Apothecary in the Imperium, next to The Emperor and Eldar goddess Isha (and Apothecary Fabius if he hadn't turned bad).
- Atharva, one of the outcast dead and a powerful Thousand Sons psyker observed Arik and commented that he has an: "aura too bright to look upon. His presence had a gravity all it's own, demanding all attention and fear." and he "could barely stand to turn his psychic senses on him for fear of being overwhelmed.". Keep in mind only the Emperor and the Primarchs has that kind of aura, yet Arik, a Thunder Warrior has that kind of aura surrounding him. This also raised an interesting theory about him being the test subject of the Primarch project, where the Emperor imbued part of his soul onto a living being using somekind of forgotten psychic technique.
- He is named after Taranis, the Celtic god of... thunder. So yeah, the guy is literally a god-tier (thunder) warrior. Interestingly, this actually could be evidence of his fandom's pseudo-Primarch/proto-Primarch (the physical prototype as opposed to The Angel being the soul prototype) view of him. Because being a Thunder Warrior named after a god of thunder has some...implications.