The Wraith are a vampirous, hive-based species that harvest on the 'life-force' of other beings for nourishment through suckers on their palms. Countless worlds in the Pegasus Galaxy live in constant fear of the Wraith, who return periodically to cull their human herds.
In the fictional universe of the science fiction TV series Stargate Atlantis, the Genii are a human culture living in the Pegasus galaxy (see also: Human civilizations in Stargate Atlantis). Although they appear to be simple Amish-like farmers, the Genii are an advanced, militaristic society. In the series, they have been both enemies and allies to the Atlantis Expedition. Nevertheless, Teyla Emmagan believes that outside of Atlantis, they represent the galaxy's best hope.
In the science fiction series Stargate SG-1, the Replicators are self-replicating machines that seek to convert all civilizations into more of themselves, thus posing a dire threat to all other beings. They were first mentioned indirectly in the season 3 episode "Fair Game", and first seen onscreen in "Nemesis". The Replicators are primarily the enemies of the Asgard race, but Earth must also contend with them on several occasions. The Asurans of Stargate Atlantis are also called Replicators, due to their similarities to the SG-1 race.