In lore, the Guardians are four powerful wizards. There used to be five, and there are technically many others currently in enchanted sleep. I'll start from the beginning.
The origin of the Guardians is shrouded in mystery. The Guardians themselves remember little, and what little they remember of their past lives they have consistently refused to recount. We know that in the distant past, long before Asymptonic became stranded on the world of the Artifact, they existed in greater numbers as wicked sorcerers of terrible power. At some point, all of them passed into an enchanted sleep. They slept upright in chambers deep beneath the surface of the earth for eons.
The inner walls of those chambers were lined with runes and glyphs of power. Entombed along with the Guardians were various magical artifacts and treasures. Scattered throughout the world of the Artifact were ancient structures, believed to have been temples at one time, which had similar runes inscribed within them. These runes were later read by the Guardians after their awakening, and provided a glimpse of their past.
I digress. The first Guardian was DiabolicalMech. Asymptonic was exploring in the caves beneath the Three Sisters, and fell through an unstable floor into Diabolical's chamber. He managed to wake him, along with the second Guardian (who was sleeping in the very same chamber), mopb3. He nursed the pair of them back to health, and helped them discover their powers and recover from their sleep madness.
By this time, Slicers arriving in search of Asymp's research team had been building up thanks to the immortality provided by the Artifact, and had begun to group together and make rudimentary pastoral societies. While Asymp continued his vigil by the Three Sisters, the two Guardians acted as guides for these first civilizations. They used their powers to perform miracles, as well as teach them the ways of fire, metallurgy, cooking, herding, farming, etc.
In time, more Guardians were awoken. The third Guardian was Gallazius, and after him a number of Guardians were awoken unsuccessfully. That is to say, they did not survive the process due to the strain their bodies had undergone from their incredibly long sleep. These losses pained the first three Guardians, to the point that they were reluctant to attempt waking more, for fear of what would happen. Eventually, however, a fourth Guardian was successfully awoken, called Magpieman.
Here, I ought to give a brief bio of the Guardians now:
DiabolicalMech was the eldest of the Guardians, and the most mysterious. He was completely covered by a black cloak, so that only his eyes could be seen glowing beneath the edge of his hood. Over his shoulder he wore a multicolored sash, and was very tall and broad-shouldered. He was seen very rarely, but would occasionally appear to warn Slicers against dark magics.
mopb3, the second oldest, was the most involved in the affairs of the people. He took the form of a young boy. and personally created a number of the safe havens for the Slicers of that world. He was called Caretaker, or Protector.
Gallazius was the third Guardian, and his accumulated titles include the Midnight Sage, The Wanderer, the Lightning Mage, and the Weather Wizard. His chosen form was a dwarf with a flowing golden beard. He was prone to wandering and exploring the world, all the while guiding the people he encountered. (And while he's in this period of inactivity, I'm proud to act as Loremaster in his stead
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The fourth Guardian was Magpieman. He took the form of a man, wearing a crown and a flowing robe. Second only to mop in his active involvement in the affairs of Slicers, he later founded the kingdom of Hyrule and was actively sought after by the rulers of other kingdoms for his great wisdom.
Back to the history. The Guardians and Asymptonic met regularly, and whenever they considered waking another Guardian, they would always convene first and make the decision as a group. However, on the cusp of the First Age, Asymp woke a fifth and final Guardian without the consent of the previous four.
The fifth Guardian was called Syris. He was vastly greater in power than any of the previous four, rivaled only by Preksak and Asymptonic. He even demonstrated the ability to create matter from nothing, a feat only Asymptonic had previously demonstrated very sparingly. He took the form of a young man, very handsome, with flowing blue robes, a cape, and a tall pointed crown.
Syris was proud and haughty, styling himself the god of that world. He was a commanding leader and infinitely cunning, easily turning Slicers to his cause. At first, he was reluctantly accepted by his brothers, who resolved to keep a close eye on him. He gathered a large following to himself and used dark magics to raise a city for him and his disciples. He bound creatures from other realms to his service, and harnessed fel energies to further increase his own power. He taught his followers dark magic, and planted spies in the domains of his brothers.
His power was great enough to keep the existence of his stronghold secret from his brothers, until by chance it was discovered by Gallazius in his wandering. When he saw what Syris had done, he was horrified, and summoned DiabolicalMech, mopb3 and Magpieman. They cast Syris's followers into the Void, beyond the power of the Artifact, and smote the dark city to ashes. Finally, they confronted Syris together atop the tallest of the Three Sisters.
Syris commanded not only the power over nature and space afforded to him as a Guardian, but also the dark powers he had called to himself previously. This, combined with his natural talent for magic, made him more than a match for all four of his brothers. The battle was legendary, raging for four days and nights, the sky aflame and the earth quaking with exertion.
Finally, all four wizards combined their power to subdue Syris. They could not kill him, and so they brought him to a realm of fire and molten stone, where they bound him with silver chains of light forged in and out of time. There he remains, in eternal torment, until the end of all things.
After the defeat of Syris, the First Age dawned with the founding of the first true city, Church Town. Since then the Guardians have continued in their capacity as guides and teachers. After the defeat of Preksak and the exodus to Loka, some Guardians ascended to a higher form, now called Elders, in the crossover between worlds.
Old One is simply the title attributed to Asymptonic, nothing more.
Hope that helped.
