Knights-Errant

The Knight-Errant are/were a group of Space Marines brought together from various different Legions at the behest of Malcador the Sigillite in order to create a cadre of the best and brightest that the space marines had to offer, and use them to form a new Chapter to combat the threat of daemons and forbidden magic that the Imperium was not prepared to fight against due to the erasure of all knowledge of them as part of the Imperial Truth. Members of the Traitor Legions which refused to follow their Primarchs into corruption made up a surprisingly large part of their number; having proven themselves truly pure in the face of absolute corruption, the Knights Errant offered them a new purpose away from the taint of their old Legions.

There is evidence for both their being the forefathers of the Grey Knights and the Deathwatch. Despite what we think we know of the original Grey Knights and that eight of the companions would become the first Grand Masters of the new chapters, those that initially joined the first member Nathaniel Garro may not necessarily be destined to become Grey Knights themselves. Author James Swallow has came out and said as much himself in an interview, but beyond that we know that many members of the Knights Errant would not survive the Horus Heresy.

Known Members

Nathaniel Garro

Death Guard Captain of the Eisenstein. The first member; the guy who fled the massacre at Istvaan III and managed to bring word of the Horus Heresy to the Imperium. On the way there, he also became the first of the Loyalists to encounter what would later be known as the Plague Marines.

Garviel Loken

A Luna Wolves Captain who is very much the protagonist of the first trilogy of Horus Heresy novels, was thought dead after being defeated by Abaddon at Istvaan III and having a building collapsed on him. When Garro first discovered him, survivor's guilt had driven him half mad and he was convinced he was the only Loyalist left alive in the Imperium. Was supposedly the final member that Garro would recruit according to Malcador, although other members were inducted after Loken himself.

His major highlights include:

• Being a member of the Mournival; the four advisors to Horus along with Abaddon, Torik Torgeddon, and "Little Horus" Aximund.
• Hilariously beating Lucius in a duel, pointing out that the duel would not be about their skills in blades. He then dropped his sword and broke his opponents nose with a punch, causing Lucius' face to be marked for the first time.
• Facing off against his former battle-brother Abaddon on Istvaan III.
• Being one of the lone surviving loyalists after the virus bombing and managing to stay alive on a planet that had become populated almost entirely by Plague Zombies.

Tabletop

Currently the only member with tabletop rules in Horus Heresy, though that's his pre-Knight status: Loken is a Legion Praetor character with Initiative 6 and a Paragon Blade, with the ability to pick himself up from death once per game. Strangely he's the only Praetor with Power Armour rather than the standard issue Artificer Armour that usually comes on Praetors, though he does get an Iron Halo which usually has to be bought for extra.

Others

• Tylos Rubio - An Ultramarines Librarian who was the first member to be inducted by Garro. He was recruited in the midst of the Battle of Calth. Rubio would essentially become the Garro's second in command for several missions, and got his own job of travelling to Baal to collect all of the wargear of the Blood Angels (to give to the future Grey Knights) when everyone thought Sanguinius had fallen at Signus.

• Macer Varren - A World Eaters Captain who was one of a group of loyalist refugees that fled to the Terran Solar system, a cockney-marine and an utter badass. Surprisingly level-headed for someone with the Butcher's Nails jammed into his brain.

• Sevarian (The Wolf) - Not a Space Wolf, though artwork portrays him to look similar to one, but a Luna Wolf. He was a member of the Crusader Host (basically Space Marine Ambassadors to Terra) but was imprisoned on Terra with all bar the Imperial Fists due to suspicion. He broke out of prison and was brought back into the fold by the Samurai (not kidding) Nasagena. He is a latent psyker whose powers were unlocked by Magnus' psychic message that broke the Golden Throne, though Malcador explains it such that Sevarian uses them so instinctually that he does not know he has them, which makes him unique.

• Bror Tyrfinger - An actual Space Wolf.

• Ares Voitek - Iron Hands Techmarine.

• Fel Zharost - A Night Lords Chief Librarian who, was exiled by Sevatar after the Edict of Nikaea mostly because no-one could be bothered to care about the Librarius except Zharost himself. He somehow fled to Terra and was eventually collected for induction into the Knights-Errant.

• Ison - A Librarian, assumed Blood Angels.

• Theodor Ruttveld - A Space Wolf, was assigned to watch over Konrad Curze and ensure that the Edict of Nikaea was obeyed. Heavily maimed by Curze and delivered to Terra as a message. It is uncertain if he is to become a Knight-Errant though he he kept alive on the Sigillite's Authority and it is made clear that he it to be kept as whole as possible and not interred in a Dreadnought.

Deceased Members

As we know several members were inducted into the Knights Errant, but many did not survive, and considering that the number above is greater than eight, we know that several more will perish or find other duties.

• Iacton Qruze - One of the oldest members of the Luna Wolves and one of the few Legionaries who had been recruited before Horus was found. Referred to as "The Half-Heard" mostly because no-one was paying attention to what the old coot was saying. Got the job of overseeing the prisons on Titan for people who know far too much to be let loose in the Imperium, though is killed by Horus on board the Vengeful Spirit when an attempt at placing teleport beacons for the Space Wolves to deep strike aboard was discovered.
• Tubal Cayne - Iron Warriors member of the Crusader Host like Severian.
• Rama Karayan - Raven Guard
• Altan Nohai - White Scars Apothecary
• Callion Zaven - Emperor's Children Champion.

Grey Knight Grand Masters

We know that there were eight Grand Masters who travelled with Malcador to Titan when it was cast into the warp, unfortunately we don't yet know who they all are yet, and is made more difficult to guess since Grey Knights ritually change their names to mirror their daemonic foes. In Aaron Dembski-Bowden's The Emperor's Gift, all eight are long dead and entombed together in the Chapter's cemetery on Titan.

1. Janus - Known to us as the first Supreme Grand Master, though his original name and legion remain unknown.

Considering a bunch of circumstantial evidence One candidate to Janus' identity could (stressed "could") be the Twin-Primarch Omegon.

5. Epimetheus - A Dark Angels psyker of prodigious strength who survived into the 41st Millennium by being trapped in the Damnation Cache on Pandorax. Epimethius would eventually be captured by Abaddon and given to Fulgrim in a bid to gain the allegiance of the Emperor's Children for the 13th Black Crusade, Epimethius himself was intended to become the Avatar of Slaanesh.

His original name is unknown, but one consideration could have been Zahariel who may have joined the Knights-Errant instead of the intended membership of Cypher.

8. Khyron - First Grand Master of the Eighth Brotherhood, and with a name close to "bat" in Greek, his tomb on Titan depicts a helmeted warrior leaning casually on a halberd. The tomb's epitaph closes with "If you wish to grow wise, learn why brothers betray brothers.’. As the halberd and casual attitude was the hallmark of the Eighth Legion's First Captain Sevatar, and Jago Sevatarion was last seen in Imperial hands relearning his psychic gift at the end of ADB's The Longest Night, many Night Lords fanboys believe it is Sevatar. Having once betrayed the Emperor but then disillusioned with Chaos and Horus, could he have then betrayed his brothers in the the Eighth to return to the Imperial fold? Only ADB knows, and he hasn't gotten us that far yet.

Abaddon claimed to know of the eight original founders and stated that one was an Ultramarine while another was his "erstwhile brother". Thus it's increasingly likely that Rubio and Loken are two of the first Grand Masters.

Human Members

While not necessarily Knights-Errant, we also know that four humans were recruited by Malcador to form the founding members of the Inquisition.

• Yasu Nagasena - the Last Samurai and expert tracker who was tasked with finding the Outcast Dead, then chasing down and killing Sevarian. He was only stopped from doing so by Malcador who wanted them both for his new project
• Hassani Sabbyat - A Stormtrooper who was into the Sigillite's employ to collect an artefact from Egypt, despite being told not to look into the box, he did and was brought before Malcador to explain himself. It turns out that the artefact was the Rosetta Stone and Malcador was part of an order that kept history and learning safe and intact. He also gets shown the doorway to the Emperor's Webway.
• Katanoh Tallery - a scribe who discovered that someone was using galactic scale tax avoidance schemes to fund and build a legion sized force under the Imperium's nose and within their territory. She was aided by Garro in finding who was diverting Imperial equipment in such an underhanded manner. Turns out it was Malcador and he was pissed at Garro for uncovering the Grey Knight fortress on Titan before it was finished, but was convinced to keep Tallery in order to better manage the bookkeeping. It's unlikely she is going to end up being an Inquisitor though. (Although, looking for funny spending would be an excellent way to find heretics...)