The Arretians, also known as Sargonians, were a progenitor species who were from the planet Arret.
In its early history, the Arretians formed the Arret Empire which consisted of two different races united in a consortium. These two species had been allies for so long that they thought of themselves as a single nation. Lirahn suspected that the ancestors of both the Deltans and Vulcans may have been the Arretians based on their physical resemblance to those species. (DTI novel: Watching the Clock) Around 600,000 years earlier was a period in which the Sargonians explored the galaxy and placed their colonies. (TOS episode: "Return to Tomorrow") For a hundred thousand years, the Arretians spread across the galaxy where they terraformed and settled worlds that were remade in their image. (DTI novel: Watching the Clock) It was suspected that the Sargonians were responsible for seeding various worlds with Vulcanoid races. (TOS novel: Ex Machina) The Arretians were believed to had met a number of junior races in this time who were mentored and cultivated. (DTI novel: Watching the Clock)
At some point, the empire of Arret was established and was one of the great powers of this era. They eventually came into conflict with the Selakar during the Great Psionic War when that species used their psionic talents to bend others to their will thus allowing them to rule a hundred worlds. To improve on this talent, they created a psionic amplifier device but Siri informants told the Arret empire of their existence who staged a raid to capture prototypes of these new weapons. Upon seeing their destructive potential, the Arretians kept two of the amplifiers as weapons of last resort and hid them beneath the crust of two of their colony worlds in impenetrable bunkers where the Selakar spent decades attempting to recover them. Shortly afterwards, the Arretians shattered the powerbase of the Selakar forever and they were hunted down across the galaxy. (DTI novel: Watching the Clock)
Around 498,000 BC (reference stardate -5,000/00), the people of the highly advanced civilization on this world had thought they were as powerful as gods, but ended up destroying themselves in a world-devastating civil war. (FASA RPG module: The Orions: Book of Deep Knowledge) According to Lirahn, the Arretians were one of the great races that came to believe that they were gods and thus entitled to remake the universe in their image as they were its masters. In time, worlds were scarce for them and their ambition remained unchecked to the point that the two united races began to see one another as rivals. It was only countless generations of law and custom that prevented them from fighting one another. However, their powerful minds began to allow their subconscious desires to take effect in the minds of the younger junior races who turned on one another thus instigating a war by proxy that drew in their masters as well. This reluctant warfare led to growing resentment until open war was declared leading to the Arretians bringing about devastation to their own domain. (DTI novel: Watching the Clock) The inhabitants of the planet were engulfed in a devastating conflict that destroyed the surface of their world, leaving only three survivors. (TOS episode: "Return to Tomorrow") This war was created by energies sent out from the entity known as (*) during its battle with the Q Continuum. (TNG novel: Q-Zone)
Settlers from Arret were forced to abandon their homeworld and thus a small fraction of the species left the destruction that was brought upon by their brethren. They were chosen to live on a new planet that was later designated as Gamma Trianguli VI millions of years ago where the machine intelligence known as Vaal was built to watch over them. (TOS comic: "Devil Down Below!") Later, the Arret civilization would be the earliest known interstellar civilization for which coherent records existed, and its demise was observed by the Rigellians. The three survivors were discovered and interviewed by Federation scientists shortly before their deaths, and told of their original humanoid forms and far-flung settlements, suggesting that the races of the Federation might be their descendants (though this was considered unlikely, based on archaeological evidence to the contrary). (FASA RPG modules: The Orions: Book of Common Knowledge, The Orions: Book of Deep Knowledge)
In 2188, the USS Argonaut made contact with the planet Capella IV and learnt more of the society's history from the story in Lay of the Mountaintops which spoke of gods that placed the Capellans on their world. This led to speculation that the Preservers or perhaps Sargon's people were responsible for seeding Capella IV with life. (Decipher RPG module: Worlds) By the mid-24th century, the term Sargonian was used by citizens of the United Federation of Planets to identify the race that Sargon belonged to and they were considered one of the ancient civilizations of the Milky Way Galaxy. (TNG novel: The Buried Age)