The Suel were by far the oldest civilization in the world, ruled by sorcerers and - as the ages wore on - decadent to the extreme. The Suel are described as having pale skin, blonde or red (kinky or curly) hair, and blue or gray eyes. Frequently, they are albino. They lived far to the southwest, in a fertile basin between four mountain ranges.
They are said to have created many new races in their foul experiments with their slaves, including dopplegangers, skulks, jermlaines, and the derro. They created the artifacts known as the Orbs of Dragonkind, as well as an evil box connected to the hordes of the Lower Planes, now known as the Bringer of Doom. Some of their spellcasters learned how to become a kind of lich that takes the form of a spirit made of black fire that periodically moves from body to body as their old husks are worn out. The greatest of their arcane spellcasters were the Mages of Power, who could accomplish feats only gods can accomplish in the present era.
Their gods included both Wee Jas and Kord, as well as Norebo (god of luck and risk; Wee Jas' lover), Beltar (goddess of pits and malice), Xerbo (god of merchants and sea creatures), Phaulkon (god of archers and the wind), Phyton (god of nature), Osprem (goddess of sea creatures and sailors), Lydia (goddess of light and truth), Jascar (god of mountains), Llerg (god of beasts), Bralm (goddess of insects, hives, and obedience), Dalt (god of portals and thieves), Fortubo (who rejected them due to their mistreatment of dwarven slaves, joining the dwarf pantheon instead), Ranet (goddess of fire and the hearth, murdered by Pyremius), Syrul (goddess of lies), and Pyremius (god of fire and assassinations) - all their gods were created by Lendor, god of time and tedium.
Eventually they came into conflict with a neighboring empire known as the Baklunish Caliphate. The Baklunish were a proud, deeply religious people who believed in the immutability of fate and principles they call the Four Feet of the Dragon. They had an affinity with elemental magic and psionics, and their spellcasters were almost a match for the Suel. The war dragged on for many decades, and both sides began recruiting evil humanoids as mercenaries - orcs and hobgoblins who began rampaging and looting the realms of their employers. Both empires began disintegrating into chaos; the Suel seem to have suffered a civil war at the same time, many of the noble houses of the empire bringing all their followers, soldiers, servants, and slaves out of the empire entirely in an attempt to escape the madness and anarchy of the war, founding rude settlements in the neighboring Sheldomar and Javan river plains, and in the islands and tropics to the south. The emperor's own son fled to the other side of the continent, where he founded the Scarlet Brotherhood.
Eventually, the Suel Mages of Power decided that a final solution was necessary before the war destroyed their ancient empire entirely. They cast a beyond-epic spell called the Invoked Devastation, which completely vaporized the cities of the Baklunish and turned their lakes and rivers into a dry, barren steppe.
The surviving Baklunish spellcasters responded by gathering in an interplanar nexus, the ancient stone circles Tovag Baragu (through which Vecna would later be banished), and brought down a curse remembered as the Rain of Colorless Fire, which incinerated the entire Suel empire and covered its cities with waves of ash and dust that swept over everything like an ocean tide. All the history, treachery, hubris, and glory of the Suel was drank by what is now called the Sea of Dust.
A handful of Suel noble houses - the Rhola, Neheli, Lerara, and a few others, along with their servants, followers, and soldiers - were saved from this devastation by the Last Mage of Power, Slerotin Waymaker, who protected them with a magical barrier. With a single spell, he created a tunnel that penetrated a mountain range for hundreds of miles, and led his people to safety (except the Lerara, who hesitated inside the mountain range and ended up sealed with in it, degenerating into a race of ooze-worshipping subterranean cavefolk). Some of Slerotin's apprentices would go on to build Castle Maure, which has been the subject of many Dungeon Magazine adventures.
In their new lands, the surviving Suel made war on everyone who was already there - the indigenous Flannae, the elves and dwarves, the gnomes and halflings, the orcs and goblins - and another race that had fled the Suel-Baklunish wars - a race of olive-skinned nomads called the Oeridians. The Oeridians, though no paragons of virtue, had spent some time gathering many potent artifacts and mastering combat magics, and they were more willing to ally themselves with other races than the Suel were. In addition, they had hope - their priests had told them of a great destiny to conquer the whole of the continent, while the Suel only remembered the glory they had already lost. In the many wars that tore the continent in the next few centuries, the Oeridians came out the victors. The Suel held on to a few independent lands - the lands of the Scarlet Brotherhood (known as Shar), the icy Thillonrian Peninsula, the mysterious Lendore Isle, the southern tropics, and the mildly despotic Kingdom (later divided into the Duchy and County) of Urnst. Elsewhere they blended with the Oeridians, either as a conquered people or (in the Sheldomar Valley) as partners.
The few identifiable Suel today tend to be proud of their ancient heritage, but they're not necessarily racist (though the Scarlet Brotherhood certainly are).