Traitor Legion Loyalists

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COMPLETELY 100% LOYAL.

"Thou shalt not follow a multitude to do evil."

– Exodus 23:2

Traitor Legion Loyalists are the rare few Space Marines who, despite hailing from the Traitor Legions, stayed loyal to the Emperor and the Imperium, proving that despite what some characters in 40K think, having geneseed from a suspect source is no sure indicator of bad character. They are a very rare group of individuals given the initial purges of Loyalists elements from the Traitor Legions at the Battle of Isstvan III or by internal purges such as those enacted by “The Brotherhood” in the Word Bearers. While most of the information below has just been hints for now, this is a matter that has been popping up every now and then for the last few years.

As it happens, many of these Traitor Legion Loyalists during the Horus Heresy who did not end up in the annals of history became Blackshields, the precursor to the 40K equivalent of the same name where a Marine with no emblems or markings can petition to join with the Deathwatch on a permanent basis, no questions asked. The term "Blackshield" by itself leaves it open as to whether the individual Marine seeks to redeem himself OR his chapter if it went rogue or was destroyed. Although Blackshields are a rarity in 40K, there were enough in 30K for such a tradition to begin and survive to the present day in the Imperium.

Those groups with enough numbers, or perhaps ties to the right people, were able to pass themselves off as successors of other Chapters after the Second Founding. Or their founders purged and changed their own records, so that over time, no one within the Chapter knows who their true progenitor is (which can lead to some fun times when an Inquisitor comes across evidence that it occurred).

Generic armies of them can be fielded in 30K with the Orphans of Betrayal Rite of War. As is fitting for a rogue, largely unsupported force, the rite doesn't provide many bonuses unless you're fighting Traitor versions of the same Legion you're fielding.

Known Loyalist Members of the Traitor Legions

Note: Characters whose names are listed in italics have received rules in some form in FW's Horus Heresy releases for the 30k era. Additionally, marines who died or went missing in action (without returning later during or after Horus Heresy) in the Great Crusade like Hastur Sejanus don't count as while they are all technically loyalists there was no meaningful distinction at the time.

• Death Guard
  • Nathaniel Garro (became the first of the Knights-Errant, first to bring word to the Imperium about the Horus Heresy)
  • Andus Hakur
  • Meric Voyen (former head Apothecary of 7th Great Company. Defected with Nathaniel Garro. Renounced his vows as an Astartes following 'The Flight of the Eisenstein', slain after being possessed by the Lord of the Flies)
  • Huron-Fal (Venerable Dreadnought, chose to self-destruct rather than be killed on Isstvan III)
  • Tollun Sendek (Slain by the Lord of the Flies on Luna)
  • Ullis Temeter (Killed on Isstvan III)
  • Helig Gallor (Recruited into the Knights-Errant)
  • Bajun Kyda (Recruited into the Knights-Errant. Killed at Proxima Majoris)
  • Crysos Morturg (Became a Blackshield during the Battle of Isstvan III, survived and was rescued by Calleb Decima. He ended up surviving the entire Heresy and became Captain of the 108th Independent Company. He and his Company were eventually sent out to monitor and patrol the Ghoul Stars. Notably, this was over fifty years after the Heresy ended, implying at least some surviving Traitor Legion loyalists were utilized by the Imperium to form "Independent Companies" instead of Chapters)
  • Erud Vahn (Became a Blackshield during the Horus Heresy)
  • Juball (Died on Isstvan III)
  • Solun Decius (Succumbed to Nurgle's Rot, becoming the daemonic entity calling itself "The Lord of the Flies")
• Emperor's Children
  • Saul Tarvitz (Called "The First Loyalist" for being the first to realize the legions betrayal and helping to send warning to the Imperium. Currently MIA. Tho the authors have stated he died during the virus bombing of Istvaan III)
  • Callion Zaven (Recruited into the Knights-Errant. Killed on the 'Vengeful Spirit')
  • Argentus Kiron (Member of the Outcast Dead, slain on Terra)
  • Ancient Rylanor (Contemptor Dreadnought, KIA post-Heresy, nearly succeeded in killing Daemon Prince Fulgrim)
  • Rakishio (KIA in Sol System by traitor White Scars who failed to infiltrate Terra)
  • Solomon Demeter (Captain of 2nd Company, KIA Isstvan III)
  • Lord Commander Vespasian (slain by Fulgrim)
  • Lord Commander Abdemon (Member of the original 200 Emperor's Children Legion survivors -they had some form of non-Chaos related disaster- prior to reuniting with Fulgrim. Presumed slain on Isstvan III by traitor Astartes)
• Iron Warriors
  • Warsmith Barabas Dantioch (14th Grand Company. Defied Horus' and Perturabos' orders to betray the Emperor. Lead his garrison in the defense of the stronghold *The Schadenhold* during the the Great Siege of Lesser Damantyne. Recruited by the Ultramarines to FORTIFY Imperium Secundus. Activated the Pharos navigation/communication beacon under Guilliman's orders, unintentionally drawing the attention of the Tyranids to the Milky Way Galaxy. Sacrificed himself in a glorious battle to save the forces of Imperium Secundus. Posthumously declared a HERO OF THE IMPERIUM.)
  • Iron Palatine Zygmund Tarrasch (14th Grand Company. Survived the Great Siege of Lesser Damantyne. Recruited by the Ultramarines to FORTIFY Imperium Secundus.)
  • Chaplain Zhnev (14th Grand Company. Survived the Great Siege of Lesser Damantyne. Recruited by the Ultramarines to FORTIFY Imperium Secundus.)
  • Sergeant Ingoldt (14th Grand Company. Survived the Great Siege of Lesser Damantyne. Recruited by the Ultramarines to FORTIFY Imperium Secundus.)
  • Legionary Baubrista (14th Grand Company. Survived the Great Siege of Lesser Damantyne. Recruited by the Ultramarines to FORTIFY Imperium Secundus.)
  • Legionary Toledo (14th Grand Company. Survived the Great Siege of Lesser Damantyne. Recruited by the Ultramarines to FORTIFY Imperium Secundus.)
  • Venerable Vastopol (14th Grand Company. Venerable Dreadnought. Died at the end of the Great Siege of Lesser Damantyne)
  • Ancient Khragan (14th Grand Company. Contemptor Dreadnought. Thought lost with dozens of others in a battle against the Hrud during the Great Crusade. Reappeared along with those dozens of others in a Loyalist Shattered Legion formation during the Constantinum Incursions of the Horus Heresy. Personally killed the traitors' leader.)
  • Warsmith Kyr Vhalen (77th Grand Battalion. Led 2,800 loyalist Iron Warriors during the First Battle of Paramar. Survived. Never stopped cussing the traitor.)
  • Veteran Sergeant Titus Avvon (77th Grand Battalion. Warden Officer of Castellum Stronghold Epislon V. Survived.)
  • Legionary Zhinnon (77th Grand Battalion, 5th Counter-Armour Wing, 30th Squad. Fought for the Loyalists in the First Battle of Paramar. Survived)
  • Consul-Praevian Nârik Dreygur (114th Grand Battalion. Initially allied with the Traitors, he eventually defected to the side of Cassian Dracos of the Salamanders. Led his Iron Warriors in a successful retaking of the planet of Mezoa from traitorous Alpha Legion forces.)
  • Ancient Orgol (114th Grand Battalion. Deredeo Dreadnought. Answered Nârik Dreygur's call to arms to attack traitorous Alpha Legion.)
  • Warsmith Auric Saxton (Remained fiercely loyal to the Emperor and killed the Lord Commander of the traitorous Emperor's Children during the Battle of the Harrow Ravening).
  • Warsmith Annovuldi (Remained fiercely loyal to the Emperor and allied with the Raven Guard and helped take the planet Carandiru from the Traitor forces. Was later sent to Terra by Corvus Corax.)
  • Tubal Cayne (A member of the Crusader Host. Recruited into the Knights-Errant. Killed while infiltrating the 'Vengeful Spirit' during the Battle of Molech.)
• Luna Wolves
  • Garviel Loken (Survived the battle of Isstvan III, recruited into the Knights-Errant, rules are for Luna Wolf version only.)
  • Tarik Torgaddon (Killed on Isstvan III by Horus Aximand.)
  • Iacton Qruze (Recruited into the Knights-Errant, later killed by Horus at Molech.)
  • Severian (Recruited into the Knights-Errant. Eventually became Iapto, one of the founding Grey Knights.)
  • Nero Vipus (Killed on Isstvan III)
  • Vaddon (Killed on Isstvan III)
  • Unnamed Pre-Heresy Era Luna Wolf discovered in stasis on a Space Hulk and revived by the Flesh Tearers in M38 (Went berserk after getting an update on what happened before “borrowing” a warp jump capable vessel. Apparently now on a mission to personally put a boot in the ass of every traitorous Son of Horus he can find).
• World Eaters
  • Macer Varren (Recruited into the Knights-Errant, killed on Terra by the Lord of Flies during the Battle of White Mountain)
  • Endryd Haar (Became a Blackshield during the Horus Heresy, died fighting Abaddon at the Siege of Terra)
  • Tagore (Member of the Outcast Dead, slain on Terra)
  • Subha (Member of the Outcast Dead, slain on Terra)
  • Asubha (Member of the Outcast Dead, slain on Terra)
  • Skraal (Fought with Word Bearers to weaken their forces during the battle of Calth, slain on the Furious Abyss)
  • Ehrlen (Killed on Isstvan III)
  • Shabran Darr (Killed on Isstvan III)
  • Karnaugar (Killed by his gene-father on Isstvan III with Angron staying at his side as he died out of respect for giving Angron a wound that nearly killed him)
  • Juljak Nul "The Storm Walker" (killed on Isstvan III during a battle between the loyalist and traitor World Eaters, though not before killing several of the traitors.)
• Thousand Sons
  • Atharva (Executed by Dorn on Terra, though either he or his shade appeared to Magnus after his defeat against Russ)
  • Revuel Arvida (Fused with a fragment of Magnus and took the name Ianius, later the first Supreme Grand Master of the Grey Knights)
  • Omari Anat (captured by the Flesh Tearers, stayed their captive to test whether or not Nassir Amit would go insane and kill him despite ample evidence of his innocence, fate unknown)
  • Mhotep (Fought with Word Bearers/Chaos to weaken their forces during the battle of Calth, slain on the Furious Abyss)
  • Izzakar Orr (part of the original defense of Prospero, he was slain by the Space Wolves in a warp maze. His soul later helped the Space Wolves in M42 find the maze and rescue 200 Space Wolves who had been trapped since the Burning of Prospero. After reuniting and resurrecting his body, he learned that the attack on Prospero had been ordered by the traitorous Warmaster Horus Lupercal and not the Emperor of Mankind. He later closed the warp gate to the maze in order to prevent Magnus the Red from following the Space Wolves).
  • Phosis T'Kar (part of the original defense of Prospero. Came to his senses and realized he had been warp corrupted during the battle. He then immediately stopped fighting, to allow Constantin Valdor to execute him, rather than continue falling to warp mutations/corruption).
• Night Lords
  • Fel Zharost (Former Chief Librarian sent into exile, Recruited into the Knights-Errant. Possibly became Khyron, one of the founding Grey Knights)
  • Kasati Nuon (Aided the Raven Guard in their guerilla war against the Traitor Legions)
  • Vilnius Malik (Abandoned the Night Lords after becoming disgusted with what they had become. Joined up with the loyalist Alpha Legion warband The REDACTED.)
  • Kellendvar (Originally a traitor that attacked Sotha, during the battle he saved a White Scar from his own chaos corrupted brother. He then surrendered himself to the White Scar for execution, which he was granted.)
• Word Bearers
  • Kaspian Hecht/Barthusa Narek (Initially drawn to the Knights-Errant. Went rogue and independent of all other factions. Helped Eldrad kill off the Cabal before returning to the Word Bearers secretly with plans to assassinate Lorgar with the Fulgurite leftover from the attempted assassination on Vulkan. Final fate unknown.)
  • Volkhar Wreth (Member of the Crusader Host. Mortally wounded and forcibly bonded with a Daemon on Terra)
  • The Anchorite (Disillusioned Astartes who surrendered on Calth and was spared by Guilliman. Entered contemplation while detained and re-embraced the Lectitio Divinitatus; which he had memorized in his youth. Interred in an Contemptor Dreadnought after attempted suicide and secretly taught the contents of the book to a selected few in the Imperial Cult's Ecclesiarchy on Almace. Existence revealed during the Indomitus Crusade and somehow manifests powers of a Living Saint.)
• Alpha Legion
  • Legate Chaitan (Leader of a small fleet of loyalist Alpha Legion vessels. KIA alongside his crew and fleet on the strike cruiser Sigma by Alpharius's manipulation of the Sisypheum's crew while the Primarch was disguised as Shadrak Meduson)
  • Occam the Untrue (Leader of the REDACTED warband. Considers his legion a tool to test the Imperium. Currently interrogating a Deceiver shard bound in a Tesseract Labyrinth after a very costly battle in M42)

List of suspected chapters

• Grey Knights (Founders were initially drawn from the Knights-Errant) - Outright stated, although only from their history. While several Astartes from Traitor Legions were among the founders of the Grey Knights, the Grey Knights believe their gene-seed is derived from the prime template of the Emperor, though whether that's true is a point of contention among the fanbase (despite it being repeatedly and clearly stated in any and all Grey Knight's fluff, it's still unclear just HOW Big E made it).
• Exorcists (Official Imperial Fist successors. Classified and speculated Successors of the Grey Knights...alternatively Word Bearers) - The link to the Grey Knights is only due to a small mention by an Inquisitor....and the Grey Knights are notoriously against ANYONE messing with their gene-seed. However, their Chapter colors, scripture written on their armour, specializing in getting possessed by daemons (the Exorcists then banish the daemons from their bodies) are almost 1 to 1 with Heresy-era Word Bearers.
• Shadow Wolves (Luna Wolves) - All but confirmed. Despite not being Space Wolves successors (being listed as Imperial Fists), they use tons of Wolfish iconography (no, not that kind). Author/creator of the chapter (ADB) confirms they were created to represent the concept of loyalist Luna Wolves as a tribute to his wife Katie (who is a fan of the Luna Wolves).
• Blood Ravens The only known copies of their lineage are currently sealed under the orders of the Ordo Malleus:
  • (Thousand Sons) - Speculated links to the Thousand Sons Corvidae Cult, high number and heavy usage of Librarians (especially to look into the future to scry enemy's plans like the Corvidae Cult). Just prior to the Fall of Prospero, a psyker named Kallista Eris foresaw the future of the Thousand Sons Corvidae Cult, during which she all but states in incredibly on-the-nose dialogue they will become the Blood Ravens: "The Ravens. I see them too. The lost sons and a Raven of Blood. They cry out for salvation and knowledge, but it is denied!”
  • (Word Bearers) - Speculated, due to having the same genemutations and strong connections to names like operating in Aurelia sub-sector and Cyrene and overarching philosophy of a fanatical devotion to Truth and Knowledge. Their warcry "Knowledge is power, guard it well", is a direct quote from the Word Bearer First Chaplain Erebus, as well as sharing many other proverbs. The Blood Ravens also originate from a sub-sector which was part of the sectors conquered by the Word Bearers, before the Horus Heresy.
• Brotherhood of a Thousand (Thousand Sons) - Speculated. Minor Chapter with a tiny footnote implying heavy librarius and have a similar name. Use an "M" as their Chapter symbol, similarly to the heraldry of the Great Crusade-era Thousand Sons.
• Minotaurs:
  • (Old Lore) (World Eaters) - Speculated. Similar battle doctrine, known for being complete berzerkers in battle.
  • (Revamped Lore) (Iron Warriors) - All but confirmed. They maintain a similar battle doctrine that favours close combat but is now also focused on pragmatic, siege, and attrition warfare tactics (their special rule is a near exact match for the Horus Heresy Iron Warrior's signature special rules). Their Ancient Greek theme also matches up with the Iron Warriors' anatolian/eastern-byzantine/ottoman references, and their gene-seed is mentioned to have extremely high assimilation rates, just like the IVth Legion of old. They even have records of action dating back to M32. Edwin Brown, a playtester for the Badab War books, has also stated that the Minotaurs use Iron Warriors gene-seed. Of note: the lore alludes to the possibility of there having been another Chapter called the "Minotaurs" more similar to the old lore descriptions, being part of the 21st Cursed Founding of M36, and references to chimeric gene-seed, adding to the the confusion of it all. Presumably, the old lore Chapter had chimeric World Eater/someone else (possibly Iron Warriors) geneseed and their creation/extinction was to secretly legitimize the "original" Iron Warrior Minotaurs under the direct command of the High Lords of Terra. One of the Badab War writers said that they were loyalist Iron Warriors rediscovered during the Great Scouring in a distant garrison who hadn't received the news of the Heresy at all. They were allowed to remain under a short leash by the High Lords. Again presumably, the Cursed Founding World Eater/someone else chimera Minotaurs being destroyed in a sufficiently deniable fashion allowed the High Lords to get this secret unit formalised.
• Silver Skulls (Iron Warriors) - All but confirmed. Suspected to be from the gene-seed of the loyalist Iron Warriors, led by Barabas Dantioch, who helped defend Ultramar. The Silver Skulls are well known for siege warfare (including a rank called "Siege Captain"), masters of building fortifications (their fortress monastery is said to have impressed Rogal Dorn himself), and their Chapter iconography/colors are near identical to pre-Heresy Iron Warriors. Their Chapter records are stated as "lost" so they do not officially know which legion they are founded from, despite being Second Founding. Their gene-seed records on Terra are also locked away beyond even Inquisitional authority. The author of the Silver Skulls series has said they are successors founded from Dantioch's garrison, and were adopted by the Ultramarines (thus making them a case of the Ultramarines Connection). She has also said that their religious aspects are just due to the culture they are recruited from, and Silver Skulls from outside their main recruitment world find these traditions strange and backwards as well.
• Marines Malevolent (Iron Warriors) - Speculated. similar behaviors to Iron Warriors, some similar iconography. Extremely pragmatic, consider one another disposable, complete disregard for causalities or collateral damage, an extreme disdain for weakness, a tendency to challenge other Chapters, and they are pretty entitled little bastards. Like the Minotaurs, they take the wargear of defeated Astartes foes as trophies. They basically are the Minotaurs, if the Minotaurs DIDN'T have the backing of the High Lords. Their veteran's markings are also identical to the Iron Warrior's signature yellow/black hazard stripes.
  • Alternatively, possible Death Guard loyalists - Crysos Morturg was a section leader of the Death Guard Legion who survived the loyalist culling at Istvan III. He would later lead a force of Blackshields, and became a Captain sometime after the events of the heresy. Although the name of his Blackshield warband was never explicitly revealed, he would outright call his battle brothers "the Marines of Malevolence", and his flagship was named the Malevolence. Furthermore, the social-darwinist attitudes of the Death Guard are rather similar to the assholeish ways of the Marines Malevolent, and their irreverence for fallen brothers can be seen as a natural extension of the Death Guard's old "ideals".
    • Chimeric amalgation of multiple traitor legion loyalists? - Crysos Morturg's Blackshield warband was formed from whoever he could find in the chaos of Istvan III, and as it was both explicitly stated to be ad-hoc nor was it stated as to just what paternity his legion loyalists had, it is quite possible that the Marines Malevolent could have multiple lines of geneseed existing in their chapter. This would explain the lack of camaraderie that the Marines Malevolent have with the rest of the Imperium, as unlike other Traitor Legion Loyalists, Morturg's warband did not have any Loyalist Legion like the Ultramarines to vouch for or shelter them, and only the accomplishments of Morturg and the possible good-will afforded to the brothers-arms of the soon-to-be Knights-Errant would spare them from being purged in the scouring. Morturg's force of personality and heroism likely drew in more loyalist stragglers, who would revere him and his ideals. This possible cult of personality along with the greater Imperium's suspicion and antipathy towards them for being traitor legion loyalists would explain the attitudes of the modern-day Marines Malevolent; the social-darwinism coming from Morturg's Death Guard principles, and their insularism and hostility for the greater Imperium stemming from the persecution, distrust, and isolation that they faced as traitor legion loyalists, it would very much explain their callousness and disdain for the lives of those outside the chapter, as they could only rely on each other.
• Necropolis Hawks (Iron Warriors) - Speculated, officially listed as Raven Guard successors. Similar behaviors to the Iron Warriors, particularly pragmatic, calculating, unrelenting, brutal, and a preference for close quarters combat. Unlike most supposed Raven Guard successors, they do not specialize in stealth, ambush, or guerrilla tactics (or really use them at all). Instead they specialize in urban warfare/city assault (as in siege warfare, once the walls are breached). tl;dr - They act nothing like their supposed progenitors, but a LOT like Iron Warriors. Not like Cawl hasn't made other Primaris chapters from Traitor Legion gene stocks.
• Iron Fists (Iron Warriors) - Suspected. Only rumored to be Iron Hands successors, but colors similar to Iron Warriors. They also share their name with a known Iron Warriors warband.
• Death Eagles (Emperor's Children) - All but confirmed (origin suspected due to records of a Loyalist Blackshield warband from the Emperor's Children's Death Eagles company during the Horus Heresy) while the Chapter's recorded actions stretch back as far as M32.
• Red Scorpions (Emperor's Children) - Speculated. Have an obsession with the "perfection" of their gene-seed, to the point of being outright hostile to any they see as "imperfect". Said geneseed also happens to have a mutation rate inferior to even that of the Ultramarines and Dark Angels (purest among the loyalist legions), but the Scorpions refuse to surrender any samples to the Inquisition. There is also the fact that their armories are stacked with old-patterns of tech, such as Deimos-pattern predators, Proteus-pattern Land Raiders, and MKIV dreadnoughts; which unlike the Minotaurs, cannot be explained by High Lords favoritism. Unlike the Death Eagles or Carcharadons though, there are no records of them existing as a Blackshield force during the Heresy. The Chapter only enters Imperial records for the first time until M34, well after The Howling, and the 4th Black Crusade.
• Sons of the Phoenix (Emperor's Children) - All but confirmed (it's practically confirmed that Papa Cawl got a hold of uncorrupted III Legion gene-seed). Similar iconography. Their name also possibly references Fulgrim, who was known as the Palatine Phoenix. Known for liking to put on a show when in combat. Causing as much flash and boom as they can, like a rock star concert. They even have groupies.
• Carcharodons (Night Lords) - Speculated. Possible chimeric gene-seed. Most similar beliefs and battle doctrine to Night Lords. Often have a black and white morality, focus on shock and fear tactics combined with stealth, and their preferred tactic is to brutally and horrifically annihilate the target population (be they enemy or civilian), but leave a few survivors to go tell everyone else about what happened. Physical traits (black eyes, pale skin) similar to Night Lords. Dagger-like teeth similar to Curze's own. Mental mutations and unstable sanity similar to Night Lords. Similarly to Night Lords, the Carcharodons recruit from criminal populations. Their newest lore hints at them being at least one part Raven Guard successors; specifically the Ashen Claws, a blackshield warband that was heavily involved in the fights across the Nostramo sector during the Heresy, as the Carcharodons share the title for their leader: "Shade Lord". However, the Ashen Claws warband still exists as of M41. Notably, said Ashen Claws have flatly called the Carcharodons "traitor-born" and of a different breed than themselves or the Raven Guard. Likewise, a Night Lord officer noted that the Carcharodons seems to be a mirror of their own legion.
• Raptors (Chapter) (Night Lords) - Speculated, only rumored to be Raven Guard. Gene-seed more similar to Night Lords. While they suffer the pale skin/black eyes seen in both Raven Guard and Night Lords, unlike the Raven Guard but just like the Night Lords, they have fully functional Betcher's Glands. Their homeworld is near the Eye of Terror, but despite being a well known and active Chapter, their homeworld's name has been "lost", so no one knows what or where it is. The Chapter once blockaded a system, with the entire system's population vanishing. Anyone who attempted to investigate, even members of the Inquisition, also disappeared without a trace. While the Chapter shares it's name with Corvus Corax's attempt at making a Space Marine 2.0, said attempt ended in complete failure thanks to Alpha Legion sabotage, the mutated products of the program were all killed in battle. However, they also partially share the name with the Night Lords' "Night Raptors" formation....
• Storm Wardens (World Eaters) - Speculated. Similar preferred battle doctrine and color scheme to pre-Heresy War Hounds (armored assaults combined with close-combat infantry, blue armor with white pauldrons) (or maybe just like most Ultramarines successors). Records of their origins have been "deliberately" lost or destroyed (like the Lost Legions'). Additionally their homeworld is sanctioned against contacting the rest of the Imperium (not simply purged like a Chaos hive would have been) and is basically sealed off from the outside world. Though they are frankly more likely to be Iron Hands (the previous token "Scottish chapter"; also previously named "Storm Walkers") successors due to their "special friendship" with the AdMech and fondness for hiding inside metal bawxes. Or, like, possibly ultramarines like basically any other blue boys who use standard marine battle tactics of mechanized infantry, but they may just be the "Ultramarine Connection" counterpart to the Emperor's Spears' actual celtic sons of Guilliman.
• Executioners & Successors (World Eaters) - Speculated. Similar battle doctrine. Highly similar Chapter culture and behaviors. Iconography made of images minorly associated with the World Eaters (red, axes). Two of their three successor Chapters' names invoke more Khornite associations (Crimson Axes and Skull Bearers). Known for having some of the most brutal close combat methods, even for Astartes. A liking for decorating their armour with the flayed skin of their victims. Lineage questioned by other Imperial Fists successors due to lacking traits associated with the sons of Dorn. Known to be reclusive, only closely associating with their own successor Chapters. This isn't exactly unique among Imperial Fist successors however, and the HH black books and novels all but state that their unique culture is due to their origins in the VIIth legion's specialist formations.
• Fire Angels (Word Bearers) - Speculated. Highly similar behaviors and doctrine. Strict following of whatever rules they are given? Check, they follow the Codex to the letter. Highly Religious? Double check, they make the Black Templars seem like choir boys in their levels of religious zeal. Don't like Guilliman? Check. Their armour colors are even the same as the Word Bearers, just reversed (what the Word Bearers paint red, the Fire Angels paint silver. What the Word Bearers paint silver, they paint red). The combination of all of these traits, along with their Chapter colors) makes them essentially loyalist Word Bearers in all but name, but that's as far as the similarities go. However, they aren't the only highly religious Astartes Chapter, nor are they the only Chapter to adhere so strictly to the Codex (especially among Ultramarines), or the only "Ultramarines" successors to not like Guilliman (see the Mortifactors below). Much like the Executioners, there isn't any evidence hinting that their behavior is the result of genetics and not the cultural changes undergone by the Imperium in 10 000 years, especially considering that they are a Chapter that wasn't founded until very recently. However, much like the Minotaurs, there are noted records hinting that theirs is not the first incarnation of the Fire Angels Chapter.
• Covenant of Fire (Word Bearers) - All but confirmed. While officially listed as "Salamanders", the Covenant of Fire are blatantly Word Bearers who follow the Promethean Cult instead of worshiping the Emperor or Chaos. Their color scheme and iconography are a close match for the pre-Heresy XVII Legion, and their attitudes and behaviors are a near 1-1 for pre-Heresy Word Bearers. Seems Cawl has run out of fucks to give and is now just seeing how far he can push it before Guilliman catches on.
• Sons of Antaeus (Death Guard) - Speculated. Similar genetic traits included an unnatural hardy stock.
• Mortifactors (Death Guard) - Speculated. Similar color scheme and iconography to pre-Heresy Death Guard, specialize in night fighting like the Dusk Raiders, similar grim attitude, and have a preference for using Power Scythes (the signature weapon of the Death Guard). This Chapter is also obsessed with death. I mean really obsessed with it. Like the Fire Angels, these guys really do not like their "official" Primarch. Being a Second Founding Chapter, they could be a prime example of the Ultramarine Connection.
• Iron Snakes (Alpha Legion) - Speculated, officially from Ultramarine stock. Use combat doctrines and show behaviors extremely similar to the Alpha Legion. Similar iconography (a single-headed snake instead of a three-headed hydra). The Iron Snakes also have unusually specific design similarities to said Alpha Legion. Such as their Chapter Master being taller than usual for an Astartes, conceals his face, and has been known to swap identities. They also separate their Chapter into independent cells, just like Alpha Legion harrows. Due to being Second Founding, they are also likely an example of the Ultramarines Connection.
• Mantis Warriors (Alpha Legion) - Speculative, officially from White Scars stock. Like the Alpha Legion they operated from a series of hidden bases spread across the sector of space they were guarding rather than having a single HQ. In-setting they're suspected to be descended from the White Scars, but the source making that claim is a in-setting book written M36 by a High Lord of Terra that has been edited multiple times since then by other High Lords and multiple Inquisitors. Their tactics are more reminicent of the Alpha Legion than the White Scars, with a focus on stealth, ambushes and the like. Their colours (green and yellow) match the Rogue Trader-era AL paintjob, and FW's book mention that the Alpha Legion have been seen fighting in green power armour. They maintain elite cadres of skilled marksmen who assassinate enemy leaders, rather like the 30K-era Headhunter Killteams of the Alpha Legion. Not to mention, the Alpha Legion fought the White Scars multiple times across the Heresy and FW's version of the Chondax campaign has several hundred White Scars on recon missions "disappear mysteriously". Finally, an alternative name for the Mantis Warriors is the "Mantis Legion".
• Angry Marines (World Eaters) - They can say whatever they want about who they think their Primarch is, but the Inquisition still suspects Angron.

The Ultramarine's Second Founding Connection

The Ultramarines are confirmed to have harboured loyalist members of Traitor Legions after the Heresy, rebranding them as their own to obfuscate the newcomer's past (as for why they would do such a thing, Roboute Guilliman himself is characterized as someone who abhorred the waste of any human life (Astartes or otherwise)). Guilliman also needed all the manpower he could get when he thought the rest of the Imperium was destroyed during the era of Imperium Secundus, so giving even legionnaires from suspect sources a chance to prove themselves was a practical solution, for which in the end he was not disappointed. The penning of the Codex Astartes and the shattering of the Legions into individual Chapters would also have provided the perfect opportunity to separate the loyalist Traitor Legion elements back into separate formations (both to work more as they were intended, and to make it easier to exterminate any of them that decided to betray the Imperium at a later time). Furthermore, it is confirmed that after [REDACTED] that led to the deaths of the Missing Primarchs happened, some/most Astartes of the II and XI Legions were mind-wiped by Malcador the Sigilite into thinking they had always been part of the Ultramarines and Imperial Fists (or possibly other legions), as to not waste useful Astartes assets. This act was backed up by at least Dorn and Guilliman voluntarily agreeing to have their memories of what really happened suppressed beyond even a Primarch's ability to recall. Dorn would later have this mental block partially lifted, making it likely Guilliman did the same. So, the speculation regarding the Valedictors, Rainbow Warriors and Storm Wardens (along with the tinfoil hat addition Black Templars) being lost legion loyalists might have some truth to it after all.

Of the Chapters listed above, the Chapters that are suspected of this connection are:

• Silver Skulls - Iron Warriors
• Mortifactors - Death Guard
• Iron Snakes - Alpha Legion

Sources

Forge World Horus Heresy Rulebooks

• Betrayal
• Retribution

Horus Heresy Novels

• Flight of the Eisenstein
• Pharos
• Vengeful Spirit
• Corax
  • Weregeld

Other

• How to Paint Space Marines, pg. 86
• Apocalypse by Josh Reynolds