Ancient

The Ancients were the original inhabitants of Earth, and created the stargate network. About 5 million years ago (according to Stargate Atlantis pilot episode 1: Rising Part 1) The Ancients left Earth in a huge space-borne city, known as Atlantis. After leaving The Milky Way and arriving in The Pegasus Galaxy, The Ancients found an overwhelming new enemy, The Wraith, and so the remaining Ancients abandoned Atlantis via Stargate and returned to Earth, where the reintegrated back into human society. This is how several humans, such as Jack O'Neill and John Shepherd have "the ancient gene" required to use Ancient technology.