The Ancients first encountered the Wraith many thousands of years ago. At that time, the Ancients had established a vast network of Stargates with thousands of worlds in the Pegasus Galaxy, which they seeded with human life. They had never before encountered a race with technology that rivaled their own, until they met the Wraith.
Once awoken, the Wraith fed upon the people on these worlds -- until the city of Atlantis was all that remained untouched. The Wraith attacked Atlantis with their powerful weapons, but the Ancients' shield held. Defeated, the Ancients decided to submerge the city and leave through the Stargate to Earth.
The Wraith have a frighteningly efficient regenerative mechanism in their genetic makeup, allowing their bodies to heal themselves. Even bullet holes quickly seal themselves like evaporating water. Their regenerative abilities are so powerful that it is unlikely that the Wraith ever die from natural causes the way that humans do. The species also has advanced telepathic abilities: they can force their prey to see things that are not there, and can use their mental powers to forcefully interrogate humans.
The Keeper interrogated Colonel Marshall Sumner and learned that a plentiful feeding ground -- Earth -- exists elsewhere in the universe, but she was unable to determine where. Upon her death, the entire hive reawakened. Now that the species is moving, feeding on planets throughout the Pegasus Galaxy, no one is safe.
The Wraith use stun weapons to incapacitate their prey, so that they can feed on their victims later. Their ships include the hive ships, which can land on planets during an extended hibernation cycle, and Wraith Darts -- small, fast-moving ships capable of travelling through Stargates and equipped with culling beams for transporting their prey aboard.
Wraith hive ships are governed by queens who direct that specific vessel's mission. The Queens have a brittle relationship with one another, but regularly put this distrust aside to join forces and increase their success in a culling.
Rising, Part 1 - The Athosians tell the Atlantis recon team about the Wraith, a race that has oppressed them for generations.
Rising, Part 2 - Sheppard confronts the female Wraith and kills her, unknowingly reawakening the entire Wraith population.
Thirty Eight Minutes - The team learns that the Wraith ship has left their homeworld, and flees a Wraith attack -- leaving a Wraith-like insect attached to Sheppard's neck.
Suspicion - The Wraith use a homing device hidden in Teyla's necklace to find the recon team, attacking them in five out of nine missions. Sheppard uses the device to capture a Wraith.
Poisoning the Well - The team encounters the Hoffans, and help them develop a serum that stops the Wraith from feeding on a person -- and kills the attacker.
Underground - Sheppard teams up with the Genii on a mission to infiltrate a Wraith hive ship, where they steal a data node -- revealing that at least 60 hive ships are now on the move.
The Defiant One - Sheppard's team encounters a lone Wraith survivor who has hibernated on another world in the Lantean system since the first Siege.
Sanctuary - Sheppard's team visit Proculus, a world protected from the Wraith by an ascended Ancient.
The Gift - Teyla Emmagan learns that she has Wraith DNA in her genetic makeup, prompting her to make contact with the species by penetrating their telepathic network.
The Siege, Part 1 - The Wraith enter the Lantean system and begin to make their move on the city.
The Siege, Part 2 - The Wraith launch Darts down upon Atlantis to infiltrate the city.
The Siege, Part 3 - The Wraith armada is deflected when the Earth ship Daedalus enters the Pegasus Galaxy.
The Intruder - Low on options, the Wraith implant a computer virus into the Daedalus computer systems.
Runner - Ronon Dex is pursued to P3M-736 by Wraith eager to hunt him for sport.
Condemned - Sheppard's unit arrive on a planet whose population leaves their prison as bait to satiate the Wraith's need for food.
Instinct - Sheppard's team encounter a young Wraith female who is concealed from the planet's local population by a man who has taken on the roll of her father.
Conversion - Following his encounter with Ellia, Sheppard begins to transform into the part of the Wraith that is not human, but iratus bug.
Aurora - A Wraith stows away aboard an Ancient warship, taking the place of the vessel's first officer.
The Lost Boys - Aiden Ford launches a bold plan to prove his worth to the Atlantis expedition by gaining access to a Wraith hive ship.
The Hive - A whole new strategy in fighting the Wraith is revealed when Atlantis base learns there is mounting territorial distrust between the creatures.
Michael - The team captures a Wraith an treats him with Beckett's retrovirus, turning "Michael" into a human.
Allies - Michael and a Wraith hive approach Atlantis to form an alliance, suggesting they use the retrovirus against their enemy Wraith.
No Man's Land - Outcast by his people, Michael joins up with Sheppard and the team to take down the hive ships en route to Earth.
Misbegotten - Having turned a ship full of Wraith into humans, the team settles them on a planet and must keep them from discovering what they truly are.
Sateda - The Wraith recapture Ronon and make him a Runner on his bombed-out homeworld, leading to a final showdown with their leader.
Common Ground - Colonel Sheppard is captured by the Genii, who subjects him to feeding by a starving Wraith prisoner.
Submersion - While exploring an Ancient station deep under the ocean, the team encounters a Wraith queen who survived the war 10,000 years ago.
Reunion - The team joins a group of Ronon's friends in infiltrating a Wraith weapons lab.
Travelers - Sheppard is captured by a group of nomadic humans, and inadvertently lures the Wraith to their position.
The Seer - The Wraith once imprisoned with Colonel Sheppard seeks an alliance against the Replicators, bringing news that the enemy is wiping out entire worlds populated with humans.
Be All My Sins Remember'd - The Wraith forces allied with "Todd" form an alliance with Atlantis and the Travelers, attacking the Replicator homeworld and destroying their common enemy.
Spoils of War - Sheppard's team find a Wraith ship drifting in space, leading to a series of dark secrets about their enemy and Todd's agenda.
Midway - The Wraith briefly reach Earth for the first time when they gain access to the humans' Midway Space Station, gating warriors to Stargate Command -- only to be stopped by Ronon and Teal'c.
The Queen - Teyla agrees to pose as a hive queen to help Todd secure an alliance with another Wraith faction, only to see him kill their queen and make a power grab.
First Contact - Todd's faction agrees to participate in a gene therapy trial that could render the Wraith no longer required to feed on humans.
The Lost Tribe - Believing that Atlantis has double-crossed him, Todd takes control of the Daedalus and sets out on a mission to destroy the Attero device.
Outsiders - The Wraith arrive in a village where Dr. Beckett is working, and demand that the locals turn over a group of refugees who survived the Hoffan plague.
Infection - After Todd's hive ship shows up over Atlantis transmitting a distress call, the team discovers that he and his crew have been stricken with a disease they helped create.
Vegas - In a parallel reality a lone Wraith finds itself on Earth, hiding out in disguise while he tries to signal his people.
Enemy at the Gate - Armed with an advanced "super-hive" ship a Wraith commander takes the ship to Earth to attack it directly, only to be defeated in a pitched battle in orbit.