Taosians
An alien race flees their home planet of Taos and arrives on Earth before the dawn of human civilization. Respecting all life and refusing to become what they escaped from, the people of Taos (Et Lan Toas) hid within the ocean, avoiding man and avoiding interfering with their development. They are a logical and science focus society of peace, equality, and intellectual advancement.
History
Pre-History
Thousands of years ago, the people of Taos were a prosperous society, at least until their solar system was invaded by a interstellar battalion. The invaders never revealed themselves and pushed the Taosian people from their outposts throughout their system back to their planet. The siege last decades as one of the main strengths of the Taosians is their shield technology. Sealing their planet away in an enormous planetary barrier, the invaders lay in waiting to resume their bombardment.
One other technological advancement of the Taosian people is their genetic sciences. Their main weapons being genetically engineered creatures with various abilities from massive strength to pyro-kinesis to mind control. One of these creatures, a raging hulk of physical destruction was accidentally released. Its violent path of chaos resulted in the damaging of one of the planet's shielding pylons. This opened a hole in the barrier protecting the planet and the invaders passed through.
A small convoy of Taosian ships were able to escape and eventually made their way to planet that would later be named Earth. Upon arriving on this planet, the Taosians discovered a tribal species spreading across the world. This species had yet to advance to a point of civilization, not yet even creating a city-state, let alone cities.
Debates within the Taosian society went on for many solar revolutions of this planet, later to be called Earth years or simply years. Do the Taosians compassionately enslave the local inhabitants, using them as labor until they can be taught civilization or do they hide away until these primitives advance to a certain scientific level. Latter was eventually chosen as it best maintained the ethics and morals of their species, while the former would make them invaders.
As the human species advanced over the next several thousand years, from tribes to cities, from cities to city-states and eventually nations, the Taosian people moved farther and farther away, always staying on the fringe of human society. Although they still continued their scientific pursuits, as Taosian curiosity was known throughout their sector of their galactic arm, for being the strongest any would find.
They would study the humans similarly to a sociologist living with tribal people within a rain forest, researching their culture while not tampering with it. The Taosians would, in their language, call themselves "Et Lan Taos", which translates to "the People of Taos".
It would only be a matter of time until the Taosians realized that the primitive species were worshiping them as gods. Their city, on the fringe of human explored territory, became the destination for a holy trek. The Taosians had no choice at this point, but to live where the human population can't follow; deep below the ocean's surface.
And so, after generations and the ever evolving nature of linguistics, the humans still talk of this great city. From Et-Lan-Taos would come At-Lan-Tis, the great city that sank into the ocean.
Modern Era
With the fable of Atlantis being nothing more than a fable to the Earthlings, the Taosians lived in peace and seclusion all through human history. Rarely venturing out and always making sure they are never detected.
The people of Taos live in ocean floor, in large holes or cylinders that go straight down into the rock below. Along the outer edges are homes, storefronts and research labs. Since they exist within a material that allows them to move in all three dimensions, their people technically stay below the rocky surface under the ocean. This has allowed them to remain undetected by modern human scans of the ocean with technological satellites circling the planet's orbit.