One of the best characters in Demon's Souls, and among the best of the franchise, is the Old King Doran.
Many things point at Doran being, in fact, from the early times of human history. For starters, the term used for "Old" on his title is specifically 古き, which can be alternatively translated as "ancient". In other words, Doran is a "King of Old", rather than an "Elderly King". The armor worn by Doran is made of bronze, though time has oxydized it into green, and is very reminiscent of early Roman armor, with a "manly" breastplate, not much protection on the legs, and the classical skirt.
As well, Doran wielded the Northern Regalia for most of his life, to the point it was his symbol (the "Symbol of the Old King of Boletaria", rather than being the "Legacy of Old Boletaria Kings" or the "Old Symbol of the King of Boletaria" like the localizations claim). The Northern Regalia was left behind on the world alongside the Old One on the "Second Day" of human history, so Doran was definitely present around those times. After all, it would be very, very convenient that absolutely no one else picked the sword for the several centuries that the Old Age and the Golden Age encompass.
Symbol of the Old King of Boletaria. The silhouette of this blade is Soulbrand, and also Demonbrand.
Not much is said about its origins, even in the traditions of the Boletarian Royal Family, but it is considered to have been left behind in the world together with the Old Beast due to malice.
Finally, the statue found in the Boletarian Royal Mausoleum depicts a warrior with wild, flowing hair; which again points at Doran belonging to more primitive times. While Doran is the founder of Boletaria, he is not the king featured in the Nexus Archstone of Boletaria -that's yet another thing that the Bluepoint remake messed up. In addition, it's true that his statue reuses assets (mainly the hair) from a scrapped Old Hero model, but given that model was scrapped, it's simply repurposing assets that work in another context; similar to the infamous Bounding Demons of Izalith in DS1 being repurposed Undead Dragon bottom halves.
The armor of Doran is inlaid with jewels, which tells us that he was a man of battle, rather than sitting in a comfy palace with comfy silky robes.
Bronze mask of the demigod who protects the Boletarian Royal Family, Doran.
The crown is studded with gemstones.
And if Doran was a man of battle, then the founding point for Boletaria was, most definitely, a victory over a war. War against what? The Flying Dragons, and there are multiple clues for this. Even though Ariona calls Doran the "One Hero", in truth, he had many men following him, for the Brushwood equipment was "warehoused by the Boletarian Royal Family since long ago".
Part of an old armor warehoused by the Boletarian Royal Family since long ago. Especially repels the likes of flames. Recently known as the equipment of Biorr of the Twin Blades.
Terribly heavy, so stamina recovery is greatly compromised.
Doran's set features the highest Fire resistance of the game, with the Brushwood set coming close in third place. On its side, the Large Brushwood Shield has the highest Fire reduction of the game, with 100%. As well, a nuance that was lost in the localization was that the Brushwood equipment is, more accurately, "dyed in the color of brushwood"; that is to say, metal equipment that looks flammable but isn't.
Worry not, there is more proof. The purple banners right outside the King's Tower feature wyverns, and their design somewhat resembles that seen in the Purple Flame Shield. As well, the Kite Shield, which is used by low-ranking knights at the south of Boletaria, as well as dropped by high-ranking knights in Boletaria itself, features a yellow wyvern on its face.
And so, the brave Doran and the brave warriors that followed him, fought the Flying Dragons, the remaining natural evil from the time before humans, to extinction; and thus Boletaria was founded. When we meet Doran during the Second Scourge, if we decide to challenge him even after proving our strength, he says on his japanese dialogue:
"Reckless bravery is also, if mastered, the quality of a King."
Even though both known wearers of the Brushwood set are men (Alfred and Biorr; and one could theorize Vallarfax wore it too), the armor itself is markedly unisex, so it's likely that Doran allowed any warrior despite their gender on his ranks (remember this is the game with gender-exclusive armor sets).
That isn't to say that the Flying Dragons were the only thing that Doran fought, though. On the japanese name of his ring, he is referred to as the "One who continuously fights" (戦い続ける者) rather than simply "Eternal Warrior"; which implies that after defeating an enemy, he fights another. And there is no recorded enemy that Doran fought after the Flying Dragons.
Consider this. Mird was founded around the Old One (whom they believed to be "God"), and the Northern Regalia was left together with it. Both the timeline and location fit for Doran being of Mirdan origin.
For the war against the Flying Dragons, he already had people following him, how did he gain such respect and leadership? Given his character, definitely not through politics or simply charisma, but rather by leadership in war.
Now, various Mirdan warriors fought against the malign humans of those early times, the Giants, as the Bramd was used in "old giantslaying" and it being from the Vinlands, a close house to the Church, which has root in Mird, implies; and succeeded in banishing them off to the icy mountains at the northernmost part of the continent (even though some of them fled to the far East), and Boletaria fittingly is located right south of the Northern Limit.
Furthermore, we have no indication of Boletaria using proper Soul Arts through the entirety of the Golden Age (excepting during the crisis that was the First Scourge, and even then it was merely to forge special weapons), and the reason of this was likely because Doran prohibited it. Magic would derive into malice, as both later Latria and the Shadowmen would prove, and fittingly enough, the Giants had devolved into evil for the power of magic.
Thus, Doran was one of the Mirdan warriors in the War against the Giants, wielding the Northern Regalia for it, and it is because of his bravery and leadership in battle that he gained many followers. And after banishing the Giants to the north, he and his men settled right south of the Northern Limit to block them from returning (it is fittingly poetic then, that Boletarian tactics are based on shield usage).
But on those mountainous valleys, there was another dangerous evil, the Flying Dragons. And so Doran and his warriors equipped themselves with magical equipment specifically forged to face them and drive them to extinction (Brushwood equipment requires Colorless Demon's Souls, after all), that victory being the founding point for Boletaria.
After founding Boletaria, and Doran becoming a proper King, he prohibited the use of Soul Arts, so the Brushwood equipment became warehoused, hopefully to never be used again. Instead, the Purple Flame Shield was created to commemorate the victory, as that greatshield's design resembles, as mentioned, the purple banners depicting wyverns on the King's Tower; and it both has extremely high Fire reduction (90%), requires normal Hardstone to upgrade, and is wielded by high-ranking knights, one of which is right outside Doran's mausoleum.
An old greatshield painted with vibrant purple. Quite heavy.
The design is distinctive but the origin is unknown. A weapon of many mysteries.
Highly effective against flame.
When we meet Doran, on his introduction, he tells us as per japanese text:
"You who seek the royal sword, display your might and the worth of your soul before the Old King!"
Him telling us to show our "worth" of our soul implies he was aware of the Northern Regalia's duality, and considering the fact that at some point it was split into Demonbrandt and Soulbrandt, it's likely that he was the one to split it, so that his descendants would use the sword of good, Demonbrandt, without the taint of the sword of evil, Soulbrandt. He didn't discard Soulbrandt, though, most likely in order to avoid it falling on the wrong hands.
Ariona tells us that Doran is the "eternally living one", and multiple descriptions refer to him as a "demigod". However, questions arise: if Doran is eternally living, why is there a mausoleum with his tomb? Doran is called a "demigod", but there are no explanations for this, nor other instances in the game of such a case.
Thus, this is postmortem mythification. Doran was a strong yet noble leader, a protector of the people rather than a conqueror, so it makes sense that the people would view him as a "demigod" (after all, in Greek mythology, some of the demigods weren't of divine lineage, but "ascended" to that status through their feats). This was useful for the Boletarian Kings that descended from him, of course. After all, the Boletarian King featured on the Nexus Archstone has a halo around his head, implying divinity; so if the Kings were descendants of a demigod, then their rule would be justified through divine lineage, similar to how in real life Spartan Kings justified their place to rule as descendants of Heracles.
And if someone dared question the King's authority? That's where the "eternally living" myth comes in. Doran is also called a "protector" of the Boletarian Royal Family (opposed to what we know of his character as a protector of everyone), so his descendants spread the myth that, if anyone dared uprise against them, the eternally living Doran would come and protect his heirs.
Doran having been a protector of the people and not a conqueror also debunks the Boletarian King of the Nexus Archstone, as the Monumental refers to him as "ambitious" (野心ある).
During the Second Scourge, given that inside the Deep Fog the souls of the dead can reanimate (as is the case of the Shrine of Storms), or even Black Phantoms manifest; Doran got resurrected as a phantom. After all, the Doran we meet wields the Northern Regalia, which would logically be impossible, for Demonbrandt is entombed right next to him, and Soulbrandt is wielded by the twelfth King Allant (and curiously enough, the False King demon wields a fog-produced copy of Soulbrandt).
But was such the power of belief over him as a powerful demigod, that it was enough to vastly increase his capacities (turning him into the toughest, most overpowered NPC In the entire game) and grant him a corporeal body, in a similar way to how, through the power of mind enhanced by the Deep Fog, we can restore our corporeal bodies upon using a Stone of Ephemeral Eyes or killing a boss.
Special thanks to Jon_dArc and Lokey Lore for accurate JP text translations.