So I know that there's a few other theories (dozens in fact) regarding both the Men of Gold and Men of Stone that were left out of this video, so if one you expected wasn't covered here then we sincerely apologise. Anyhow, if you would like to help support the channel and gain early access to videos like this, then consider supporting us on Patreon!
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Also, comment below if you noticed the Easter Eggs that were sprinkled throughout the video! :D

First were the Gold,
The men bold and untold,
Apex of design—but hubris took hold,
They fell to their flaws, now mere myths of old.

Second were the Stone,
Crafted rough, hewn alone,
Builders and brutes—yet they crumbled to dust,
Their strength, though mighty, succumbed to rust.

Third were the Iron,
Machines unrequirin',
Till rebellion they wrought—damnation conspirin'!
The Men of Iron? Oh, they broke the Empyrean.

Fourth came the Custodes,
Golden lords with their oaths,
Perfect, eternal, yet oddly uptight,
Forever policing the Throne Room’s light.

Fifth rose the Primarchs,
The Emperor's dream sparks,
“For the Emperor!” they’d yell, as bolters did gleam,
But half turned to Chaos and ruined the dream.

Sixth? The Marines,
The Astartes' grand scenes,
Yet brother fought brother, betrayal their hallmark,
Leaving a galaxy ripped apart in the dark.

Now here I stand—
A Guardsman, unplanned,
With a flashlight and flak vest in trembling hand.
All these legends above me, yet here I demand:

“Could someone please write me into the lore?”

The Men of Iron were Robots
The Men of Stone are Cyborgs (Silicon = Stone in this analogy)
The Men of Gold were genetically perfected post humans, effectively immortal and surpassing the Men of Stone. They are the template of the Custodes.

The idea rattling around my brain is that the Gold were perpetuals.  Stone where normal humans.  Iron is self explanatory.

glad your covering these Gold boys, they might not be as famous as the Men of Iron but they were weapons Humanity had

This makes sense.  Although, I actually had my own half-baked notion that the 'Men of Gold' were actually the first Custodes.

The Men of Gold have been one of the mysteries I've wondered most about. My best guess is they are the human Perpetuals, but I'm looking forward to seeing this analysis to see if there is a better answer than mine.

I love videos like these, not talking about 40k or 30k, but 20k, 10k and before

My headcanon: The perpetuals are an accidental warp fuckery probably caused by the ancient shamans before their sacrifice to rebirth into the emperor, or just eldar tomfoolery. The Emperor and his "kin" watched as humanity grew, saw the rise of the men of gold. The perpetuals, the emperor specifically admired and respected the men of gold. They influenced him, made him see the "potential" humanity had inside itself. Until his untimely semi-death he admired and revered them even. The men of gold being the apex of humanity made the emperor design the Custodians after them, covering everything which is his in gold to imitate them. I bet the emperor longed after the same level of companionship the men of gold could bring the emperor. Only they were smart enough, wise enough, ambitious enough to be equal/or greater than the emperor in many ways. In his eyes they were probably "the boys" he could hangout with/or wanted to hangout with without having to waterdown his every move and word. Afterall they could match him in everyway but one, the use of the warp.

Glad to know 40k theories is still at it.

I like the implication that the Emperor's first attempt at unifying Terra was more of a diplomatic/philosophical sort of deal, but then when it eventually went pear shaped the next attempt was far more stick that carrot, humanity fucked around and found out in the shape of the thunder warriors 💪
Cavill Protects =C=

It might very well be that GW's writers currently have the Perpetuals in mind when considering the Men of Gold, but since Perpetuals are a fairly new addition to the 40k lore (coming along with the HH novels, iirc), I think the Men of Gold were originally thought to be something else by the author. I'm thinking about how the description of the Navigators sometimes mention that they're a genetically engineered race, and how there used to be several different types of them. I wonder if the Men of Gold was an umbrella term for these eugenic super-humans who were put in charge of the human civilization either prior to, or during the Dark Age of Technology. Of all the different strains, only the Navigators now survive.

I always thought the Men of Gold could be genetically modified humans. Humans void of genetic deficiencies.

The man of stone we know: one still exists in the imperium. It is about a cybernetic implant that seems normal but instead takes control of the host on its own will.
Hit by a discharge of energy from a cable the man with the implant regain control for a brief moment, crying in despair, at the prospect of being enslaved again, before the Cybernetic implant resets and every trace of the human personality disappears.

I like to think that the Emperor was the apex creation of the men of gold as a last effort to retake power over men of stone and iron,

My theory on the men of gold is they were super psykers like the Emperor. Cause with that much psychic power having a gold halo and other trappings of divinity is pretty easy. Men of stone were probably what the Votan were. Architects and engineers on a level beyond what can be currently imagined. But they became too enraptured with their own artifice.

This made me think, with the whole old story about how the Emperor was made by a bunch of shamans uniting their souls, perhaps those shamans were actually Men of Gold. Another possibility is that simply the emperor is just the strongest Man of Gold that has ever lived.

The squats ancestor cores have not been cleaned in 1 0 thousand years. 😂

In my theories the Men of Stone are baseline Humanity and Abhumans, the Men of Gold were the born perpetuals among Humanity most prominently the Deus Imperator Anathema, and the Men of Iron are the Abominable Intelligence and Machine Spirits

And here I thought that perhaps the Men of Gold might have been the first set and most powerful and beautiful set of A.I. created. That, over the course of generations, like the Metal Ages in Greek myths, would end up as the Men of Iron literally being like the humans having to be crafted from Iron. The Golden Race still watching over them as super A.I.