Yuan-ti

Long before the Elves came to dominate Kyrnia, before the Dwarves had mined their first gem, before the Humans, the Halflings, or the Gnomes had taken a breath, the Middle Lands were populated by the Yuan-Ti.
Created by Ssislitheliss, a handmaid to Xi the Dark before the sundering of the gods into the Risen and the Fallen, Xi presented the Yuan-Ti to her husband Anno, as a gift to serve the gods. At first the Yuan-Ti were accepted and they served the gods with honor. Other gods and goddesses, on seeing the Yuan-Ti began creating their own servants - the Aboleths, the Djinni, the Dragons, and more where created to serve the gods in various roles, and they all served well, but the Yuan-Ti were the favored of the gods as they were the first.
When Xi was cast out of the Upper Lands, all of the gods and goddesses who supported her were cast into the Lower Lands with her, but the servants that had been where cast down to the Middle Lands as futher punishment to the Fallen, for they were not now worthy of even having servants.
The Yuan-Ti were the most numerous, and also the best equipped to deal with teir fall from the Upper Lands. When they arrived in the Middle Lands they began building, preparing for the day when Ssislitheliss, and Xi the Dark would escape the Lower Lands and rescue them from the Middle Lands in the conquest of the Upper Lands and their return to power. Thankfully, that day has not yet arrived.
But while the Aboleths hid in the depths of the seas, and the Dragons found caverns and sleep, the Djinni built pleasure palaces in the clouds, the Yuan-Ti built civilizations, cities and monuments to their lost gods and worked to free them.