The history of the Qiraji and Nerubians haven’t been completely explained. There are still things in the dark lorewise.

There are two general theories made by fans concerning the Qiraji and the Nerubians.  The first Theory was well explained by Ghostwalka @ Argent Dawn:

Long ago, during the time of the first Troll Empire, there was a race of Sentient Insects known as the Aqir.

They were spawned as many other races were spawned, and among them they included all facets of insect life; Wasps, Scarabs, Beetles, Bees, Spiders, Scorpions, Ants, and others.

They wished to destroy all non-insect life on this planet and attacked the Amani Empire time and time again. However, thanks to the power of the Troll Race in the form of their innate regenerative abilities and knowledge of Voodoo and Loa Spiritualism, they were beaten.

The Aqir Empire split in two. One went to the farthest south reaches of Kalimdor, the other to the North and across the sea to what would eventually become Northrend.

The ones who fled north are the Nerubians, and we know their sad story all too well. Their race is almost gone now, save for the living colonies yet to be hunted down and enslaved by the Lich King.

The ones who fled south were known as the Silithid. The Silithid, with their ant and wasp-like nature of hiving and burrowing into the depths of the earth… found something.

That was the remains of the Old God, C’thun.

C’thun; a husk of what he once was. He was and is a Forgotten One… a remaining part of an Old God that the Titans failed to destroy in the long ago.

C’thun took the Silithid for his own, dominating them with a mind older then any on this planet. C’thun used his powers to transform them into Avatars of what he once was, while keeping their insectile nature in tact.

The ones who became C’thun’s Avatars are now known as the Qiraj, and serve him.

And now C’thun seeks to regain his full power and body, and a might capable of reshaping the world as he did of old, and for that the Qiraj have prepared long for. Now we, the Horde and the Alliance, fight to stop them before it is too

late…

…And the Old God is unleashed on our world…

The Second Theory:

Something we have to take in consideration is that the Qiraji and the Nerubians – both – build Obsidian Statues and Sphynx(Destroyers) constructs. So … we have to assume that the Qiraji and Nerubians were both created by C’thun.

Both the Qiraji and the Nerubians come from the Aqiri—which is supposedly what few chosen Silithid became into when C’Thun used them as a template.

This is not entirely assumption. The book of The Two Empires says:

Eventually, due to the troll’s persistence, the Aqiri Kingdom split in half as its citizens fled to separate colonies in the far northern and southern regions of the continent.

Two Aqiri city-states emerged—Azjol-Nerub in the northern wastes, and Ahn’Qiraj in the southern desert. Though the trolls suspected that there were other Aqiri colonies beneath Kalimdor, their existence was never verified.

So … to recap. The Silithid is a race that was born like any other species with the Well of Eternity.

C’Thun the Old god jumpstarted the genetic code of some Silithid insects transmuting them as a template for his creation—the Aqiri.  The Aqiri then used the Silithid as a slave race.  The origin of the Aqiri (Qiraji and Nerubians) may be found through in-game quests of World of Warcraft.  Here is a collection of lore details.

Somewhat, the Aqiri suffer transmutations that split the Aqiri into two sub-races: Nerubians and Qiraji. As centuries and thousands of years went by, the transmutations became more evident.

This seems to be the most acceptable assumption—because we are aware of both sub-races having knowledge of how to create Obsidian statues, both sub-races or at least Nerubians are known to have undergone transmutations. These tidbits of info are important.

Not everyone has the Warcraft RPG: Manual of Monsters—so that will be confusing to some fans. Therefore, I will quote it for their benefit:

Quote from Manual of Monsters:

Azjol-Nerub contained huge libraries of literature, philosophy, and arcane lore. Occasionally, the kingdom would kidnap humans and elves for experimentation.

There above, we have that tidbit about experimentation with humans and elves.

Crypt Fiends of the Scourge are raised mummified Nerubians. And the Manual of Monsters throws in additional tidbits of when they were once Nerubians far before the Lich King arrived to Azeroth.

QUOTE from Manual of Monsters:

The original crypt fiends, the first to navigate successfully the difficult and dangeroous transmutations, were ancient lords of the spider kingdom of Azjol-Nerub.

It is interesting to hear the word transmutation in both the Crypt fiends and the Nerubians’ past—thousands of years before the Undead Scourge arrived.

In the Qiraji we also see the differences between themselves—the flying guards that look like humanoid wisps, Buru the Gorger, Kurinaxx, Rajaxx and his warriors, even the twin Emperors.

There is a hint that they have undergone their own transmutations, and experimentation by absorbing genetic code from the elves or other species.

By the way, Buru the Gorger looks pretty much like the Ancient Lords of the Nerubian empire—Sorta like Anub’arak.

So having all these similarities between the Nerubian and the Qiraji—I would say both races split genetically from a common template—the Aqir—which was originally C’Thun’s creation by using the Silithid as vessel/template of what would become his servants.

This is hard to understand using the word template. For example, the Night Elves could be compared to the Silithid.

They made the Highborne a template to create a new race made at the image of the Old gods—- the Naga. By the way, Knaak confirmed it yesterday. The Old gods created the Naga. It was hinted in the book, but not completely clear since we didn’t hear Azshara accepting the proposal. Now it is confirmed.
——-

Hope there is not much debate and that I came as close to what could be the intended lore by Blizzard.

So … here I will enter even more darker waters of the lore that has not been at all been explained by Blizzard. Most of what you will read below is assumption and speculation.

We know both the Qiraji and Nerubians have similarities as creation of C’thun. However, there are a major differences.

1. The Qiraji in Silithus are close to the reach of C’Thun following orders.

2. The Nerubians are independent from C’Thun, have a strong will—with immunity to mental commands (The Lich King Ner’Zhul wasn’t able to control them during the War of the Spider)—they have huge libraries of music, literature, philosophy, arcane lore. The Qiraji lack all that.

3. Anub’Arak—in Warcraft III: Frozen Throne—is one of the Ancient Lords of the Aqiri—that led the Nerubians in Northrend. He says the Faceless Ones to his knowledge was only a legend. However, he trembles in fear and recognizes the Forgotten One.

This is shrouded in mystery. There was no further details in the Frozen Throne expansion about the Faceless Ones, their past or their connection with the Nerubians.

However, we do know the Faceless Ones are servants of the Old gods. I think I heard somewhere they are children of the Old gods.

Then we have the tidbit of info that the Forgotten One looks exactly like the eye of C’Thun in Silithus’ 40-man raid zone at Ahn’Qiraj.

What I can assume from these tidbits is that something happened thousands of years ago. There are two options:

A. Speculation: Malygos, the Sundering or something caused the Faceless Ones and/or the Forgotten One to be sunk alive in imprisonment beneath the icy depths of Azjol-Nerub—thus they were no longer able to control the Aqiri-Nerubians—and therefore the Nerubians became independent from C’Thun’s influence for thousands of years—growing Libraries of music, philosophy, arcane lore.

B. Second option is that the Ancient Lords of the Aqiri Nerubians raised in civil war against the Forgotten One and the Faceless Ones, imprisoning them beneath their Kingdom of Azjol-Nerub.

Both options above sound acceptable. However, I can’t forget the fact that Anub’Arak thought of the Faceless Ones as legends. If he is one of the Ancient lords, how comes he doesn’t remember them? Anub’arak might be born after the Faceless Ones were imprisoned? That could be a reason why he doesn’t remember them.

Throughout the Undead Campaign there are many earthquakes.  These are sequel earthquakes triggered previously by Illidan.

Illidan used the Eye of Sargeras artifact at Dalaran to cause earthquakes in Northrend with the goal to crush the Icecrown and to destroy the Lich King. (Reference)

However, the earthquakes accidentally cracked the icy prison of the Faceless Ones and the Forgotten One.  The Quotes below are from the Campaign Mission:

Baelgun(dwarf, friend of Muradin Bronzebeard): I won’t let ye through this door, traitor. The recent quakes have awakened dark things under the ice … ancient, horrid things. We’ve vowed to keep them locked where they are.

The ice cracks, and horrific noises erupt from the depths of the Old Kingdom. Though the horrors within this place are fierce you must fight your way through to the exit. Let nothing stand in your way.

Anub’arak: They are the horrors the dwarves spoke of. I thought they were only legends.

King Arthas: What?

Anub’arak: They are the Faceless Ones …

Anub’arak: It cannot be … A Forgotten One. Look to your defenses, death knight! Fight as you’ve never fought before!

MAIN QUEST
The Forgotten One
– Kill the Forgotten One
– Arthas and Anub’arak must survive

Bursting forth from the ice, an unfathomable horror of a long forgotten time has emerged to block your passage. Destroy it and break free of the Old Kingdom.

As you see there is not much lore or details surrounding them.  What we know is that Illidan accidentally set them loose with the Earthquakes, and they came from beneath the subterranean kingdom of Azjol-Nerub.

This compilation of lore tidbits and speculation was meant to be informative, but also to raise awareness and to create fair debate and discussion. There is no official lore on the Faceless Ones and their connection with the Nerubians.

During the Q&A with Luke Johnson—author and developer of the new line of World of Warcraft RPG Books—he revealed that Wow RPG: Lands of Mystery and Wow RPG: Monster Guide will talk about the Nerubians and other monsters related to them. He didn’t want to specify.

Aaron Rosenberg, popular Star Trek, Warhammer and D&D book writer, who is done work for the Warcraft RPG Books too, recently told us in the public Q&A that he was assigned to do the Nerubian and Northrend creatures’ lore in the upcoming World of Warcraft: Lands of Mystery—from the point of view of Brann Bronzebeard.  So expect a bunch of new lore.

So I recommend reading them when they are released, as they are current with World of Warcraft, and might offer further details.  You can pre-order both books at our Store:
https://www.blizzplanet.com/content/97/

You can read he Frozen Throne Campaign where Anub’Arak found the Faceless Ones and the Forgoten One here:
https://www.blizzplanet.com/content/326/

Below is the Forgoten One—- looks like the eye of C’Thun