Arcanites are post-human servants of the Wizard King. They’re humans who were warped, augmented, transformed-by or just-exposed to way too much of his arcane power. They look mostly human, but have odd cosmetic changes that mark them as something unusual—skin like polished silver, gemstones embedded in the face, glowing runes instead of eyes, and so on. Each arcanite clan was charged with maintaining or operating some magical masterwork of the Wizard King. Often, they lived in underground chambers or even extradimensional spaces made with magic.
After the fall of the Wizard King, scattered arcanite colonies survived in these hidden vaults. Some hid from the world, fearing they would be punished for serving the tyrannical Wizard King. Others ‘stayed out of politics’ and just kept performing their duties, polishing the arcane crystals and reciting the same incantations generation after generation. Still others were frozen in time when the Wizard King died, locked away in temporal pockets.
In the 13th Age, surviving Arcanites might serve the Lich King (“he’s still our master, even if he’s dead and insane”), switch their allegiance to the Archmage (“we were made to serve the whims of eccentric wizards”) or just stay hidden, in case adventurers come to loot the magical machinery they were bred to protect.