The Dark Mechanicus.
It is a faction of tech-priests who defected from Mars at the end of the Horus Heresy.
Many are unaware of it in the current era due to the censorship of archives by the Departmento Munitorum. Nevertheless, the high ranks of the Imperium know about it.
The Emperor of Mankind was not only betrayed by his favorite son; during the Heresy, he was also stabbed in the back by his most reliable official partner.
Mars.
To understand how the second most powerful faction of the Imperium ended up trying to kill its Omnissiah, one must go back in time.
Specifically, before the legendary Great Crusade.
When the Emperor was not yet seated on the Golden Throne and had not fully pacified the Sol System,
he traveled to Mars.
The purpose of this journey was to rally the tech-priests to his cause and to accelerate his plans by using the technological knowledge preserved on the red planet.
From this journey, two things were born:
the title of incarnation of the Omnissiah and the Treaty of Olympus.
The first designates the Emperor as the living incarnation of the Omnissiah, whom the Mechanicus cult worships.
As a result, the Emperor was the physical aspect of the Machine God for the eccentric priests of the red planet.
The second was more complex.
The Treaty of Olympus granted political autonomy to the Mechanicus of Mars and its Forge Worlds scattered across the galaxy during its expeditions to recover humanity's lost knowledge.
The Emperor also granted an exemption to the Imperial Truth so that the Mechanicus Cult could continue to practice its faith in the Machine God — and by extension, in him as well.
The Imperium would also provide six Navigator Houses and new "Astropathic Choirs" to the Mechanicus so that it could easily unify its vast empire of lost Forge Worlds and continue its sacred quest to recover the lost STCs across the stars.
In exchange, the Mechanicum would provide the Imperium of Mankind with the weapons, starships, equipment, and technicians necessary to launch the legendary Great Crusade in order to reunite all the human-colonized worlds in the galaxy under the banner of the Imperium.
To symbolize the alliance created between Terra and Mars, which marked the true birth of the new Imperium, the Emperor changed his personal emblem.
Originally, the Emperor represented himself with the Imperialis Raptor. However, he switched to the Aquila,
a two-headed eagle.
(Image)
The heads represented the two foundations of the new interstellar human government: Terra and Mars,
the Imperium and the Mechanicus cult.
Unfortunately, misfortune struck in the person of Horus.
The latter exploited a growing resentment in the cold hearts of the tech-priests. Normally, the Imperium did not interfere in Mars's affairs.
However, there were exceptions:
the study of AI, the study of the Warp, and the manipulation of the human genome under Imperial authorization.
Horus already knew that a great many tech-priests hated this breach of the Olympus accords, but the Emperor used his status as the incarnation of the Omnissiah to circumvent them.
The Arch-Traitor used this resentment to offer a much more flexible agreement than the one the Emperor had proposed in the past.
If the Fabricator-General helped him usurp his father's throne, Horus pledged to fully respect the Olympus accords.
He even declared that the title of incarnation of the Omnissiah would be erased, but that the doctrine of the Omnissiah would remain within the machine itself.
Fabricator-General Kelbor-Hal accepted the deal.
The result was a civil war of colossal scale, as well as the loss of invaluable knowledge and the permanent weakening of the Mechanicus.
Unlike Horus's defeat on Terra, the faction of the former Fabricator-General of Mars had not completely lost the civil war.
The former Fabricator-General Kelbor-Hal is still listed as missing to this day.
His faction also left Mars with as much knowledge as possible, taking advantage of the confusion of the civil war on the red planet.
Some heretical tech-priests formed Forge Worlds inside the Eye of Terror after the Horus Heresy.
Others engaged in abominable practices with Warp entities.
This entire tragic situation meant that Terra could no longer trust Mars.
Roboute Guilliman altered the Olympus accords. Following this decision, the Mechanicus lost a good part of its autonomy.
Thus, the Adeptus Mechanicus and the Dark Mechanicus were born.
"I don't like the idea of dealing with the Dark Mechanicus, but they are certainly more flexible than their counterparts," Atreus thought as he walked through his ship.
Atreus did not trust the Dark Mechanicus.
Unlike their Adeptus Mechanicus counterparts, the Dark Mechanicus has no central figure of authority.
The former at least has the current Fabricator-General of Mars as a nominal supreme leader, who ensures a certain ethical limit.
On the Dark Mechanicus side, there was no longer anything like that to manage these tech-priests.
They had become too similar to the other traitors within the Eye of Terror.
No real central figure.
Therefore, no authority.
No rules.
A few Dark Forge Worlds might form an alliance or serve a Chaos warband, but they remained disorganized and highly autonomous.
This situation made them very flexible in their view of technology and research, but also untrustworthy.
These tech-priests had no moral limits.
Atreus could not lower his guard.
"I hope this Magos can also help with a new ship," Filon muttered as he walked.
The two Space Marines finally arrived in the reception hall prepared for the meeting with the other party.
Atreus and Techmarine Filon stood waiting for the tech-priest.
The reception hall had no windows on any of the four walls; the chairs and tables were made of steel, without cushions or leather on the seats.
There was neither food nor drinks on the tables.
The only element that could be called decoration was a wool tapestry depicting the emblem of the Iron Warriors Legion hanging on the wall.
Everything was so cold and so hard, and yet this was indeed the reception hall of Atreus's warband.
Even though the former Terran did not realize it, he was heavily influenced by the gene of the Primarch of the IVth Astartes Legion.
He cared more about the efficiency of an object than its decorative appearance.
Anyway, he had become an Astartes; those of lower rank were not worthy of being received, and those who were did not care much about such trivialities.
Unless they were Ultramarines, Blood Angels, or Emperor's Children.
The sound of a door opening echoed as Atreus reflected on the ship's coldness.
The first to enter was an Astartes in black Mark IV Maximus power armor.
The Space Marine's power armor was plain, but the protection on his right arm was equipped with a massive device, adorned with a prominent short chainsword and an adamantium drill, even integrating a laser cutting device.
This apparatus indicated that he was a Space Marine occupying the role of Apothecary.
The Apothecary stepped forward and extended his arm; Atreus responded, their ceramite armors clashing with a dull sound.
They gripped each other's arms, expressing brotherly affection.
"Welcome home, my dear Discordia." Although his face betrayed no emotion, Atreus was delighted by the return of the last member of his warband.
The Apothecary replied in a more expressive tone:
"My brothers, what joy to be back," he said to Atreus and Filon.
The two nodded.
Unfortunately, their meeting was not solely about a reunion.
"I also managed to bring Magos Morlock, who also happens to be my mentor," he explained, stepping aside a little.
Immediately afterward, a shrill metallic grinding sound echoed through the reception hall.
A massive "creature," covered in a rust-red cloak, entered the room with slow steps.
It easily measured nearly three meters and possessed fourteen auxiliary limbs, similar to the legs of a centipede.
Each of these legs moved rhythmically to propel its body forward, like a crawling insect.
There were also mechanical arms and steel tentacles undulating intermittently from its mechanical body, while its head had been transformed into a complex device.
Eight pairs of red bionic eyes, similar to those of a spider, observed the Astartes.
Atreus had already dealt with tech-priests before.
However, he was still shocked by this one's dehumanized appearance.
He forced himself to step forward and showed respect:
"Greetings, Magos Biologis Morlock. I welcome you," Atreus began in a humble tone, then continued.
"And thank you for being the mentor of my brother. I know that at the time, I did not provide a great deal of immediate advantage for his training."
The Magos's head trembled slightly; its eight pairs of eyes emitted several focusing sounds and binary language.
Finally, a distorted voice was heard:
"Young Lord of Steel, as a representative of a Forge World, I am pleased by your hospitality. However, I have come solely to deliver the surgical modification equipment, and this apprentice has completed his training."
"Please honor your word and finalize the transaction."
Magos Morlock attempted to activate his emotional simulation circuit, seeking to increase the success rate of the transaction.
The Magos's emotionless voice was tinged with artificial emotion.
"Indeed, we will fulfill our part of the agreement and demonstrate sincerity," Atreus replied with a nod.
"However, I would first like to see the merchandise," he subtly demanded.
The Magos's logic circuits indicated that the success rate of this transaction reached 66.36%, as Atreus's tone contained no ill intent.
He clearly had no intention of pulling a dirty trick on him.
"Young Lord of Steel, I am here on the orders of the Fabricator-General to deliver the down payment and fully represent my Forge World. It is unnecessary for me to attempt to deceive you," he said, opening a connection interface that allowed an experienced enough Techmarine to verify the cargo through the Magos's data.
This action allowed a sufficiently experienced Techmarine to check the cargo using the Magos's data.
Atreus turned his head and signaled to Filon.
The Techmarine took a sealed metal box from his belt, opened it with his DNA code, and pulled out a transparent chip.
This was the reason Magos Morlock had accepted an Apothecary apprentice even though he was not a pure tech-priest:
an STC template.