The Ancients are an alien species from Stargate. They were Alterans who left their home galaxy for the Milky Way and seeded it with life. They are one of the most advanced races known to have existed, having evolved for millions of years prior to the present day and reaching their level of technology long before humanity evolved on Earth. They are best known as the builders of the Stargates, Atlantis, and Destiny. Most of the Ancients have ascended to energy forms in a higher plane of existence with near infinite knowledge and powerful abilities.
It is not known if they referred to themselves as Ancients while they were living on Earth several million years ago. It is likely that they began to use that name after their return to the Milky Way when they would have been ancient compared to the relatively young species of Humans who had populated Earth.