The Wraith are an alien species, native to the Pegasus Galaxy, that feeds on humans by drawing the life force from them. Millennia ago, the Ancients had left their home in the Milky Way to settle in the Pegasus Galaxy, and there they had established the city of Atlantis. The Lantian civilization flourished, but they faced a war with the Wraith, the other dominant race in the galaxy. Besieged by the Wraith, the Lantian Ancients abandoned Atlantis and left the Pegasus Galaxy more than 10,000 years ago to return to the Milky Way, and the Wraith have continued to feed upon the human civilizations left behind. With the arrival in the Pegasus Galaxy of the Atlantis expedition under Dr. Elizabeth Weir, the Wraith have also become the enemy of Atlantis and the Stargate Program.
SG-1 encountered the Wraith during the mission to Atlantis to block the Ori supergate by establishing a wormhole connection to a black hole in the Pegasus Galaxy. As the Odyssey drew closer to the accretion disk of the black hole, their sensors and communications were affected, and they were not aware that a Wraith hive ship was approaching their position. As Odyssey attempted to detonate a warhead near the active stargate in space in order to force a wormhole arc to the supergate, the ship came under fire from the Wraith. However, Odyssey was able to beam the last two warheads aboard the hive ship and lure it toward the stargate. The explosion that destroyed the Wraith hive ship also forced the wormhole to arc. Not only was the mission successful, but as the wormhole jumped to the supergate, the resulting kawoosh also destroyed an Ori warship waiting near the event horizon.
Episode Reference: The Pegasus Project