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The Asurans are a fictional race in the science fiction series Stargate Atlantis that bear many similarities to the human-form Replicators of Stargate SG-1. These similarities have led the Asurans to simply be called "Replicators" by other characters on the show. They are first introduced in the season 3 episode "Progeny".
The self-replicating nanites that would eventually become the Asurans were created by the Ancients on the world of Asuras (M7R-227), as a weapon against the Wraith. As they grew in numbers and sophistication, they assumed the form of their creators. The Ancients programmed the Asurans with an aggression rivaling that of the Wraith, but when they determined that the Asurans would never become the weapons they desired, they destroyed their experiment and deleted all references to it in their database. A few nanites survived, however, and rebuilt their civilization on a grand scale. As per their programming, the Asurans attacked the Wraith, who were able to deactivate their attack command using a computer virus and cause them to withdraw to their homeworld. A minority of Asurans, led by Niam, are interested in Ascension.
The existence of a second advanced enemy in the Pegasus galaxy is first hinted at in the season 1 episode "Hot Zone", in which the Atlantis Expedition encounters a nanotechnological pathogen that infects and kills several personnel, but did not affect those with the ATA gene. In season 3, the Atlantis team makes first contact with the Asurans. Upon learning that they have occupied Atlantis and are the Ancients' favored "second evolution" from Earth, the Asurans launch an attack on Atlantis. The Atlantis team foils the attack after Dr. Rodney McKay accesses their base code. However, his tampering also allows the Asurans to override the programming that prevents them from harming the Ancients. This becomes evident when the Asurans launch a second attack on Atlantis in "The Return", which at that time had been reclaimed by Ancients. The Asuran strike force occupies Atlantis until they are defeated by the former Atlantis team.
The Asurans eventually begin constructing a fleet of ships on their homeworld. Believing them to be a significant threat to the Atlantis expedition and Earth itself, the SGC dispatches the battlecruiser Apollo to launch a preemptive strike on Asuras using the Horizon weapons platform. In retaliation, an Asuran satellite weapon arrives over Lantea and attacks Atlantis, forcing the Expedition to launch the city into space to escape. When the city runs low on power before reaching its destination, the Atlantis team raids Asuras to obtain a ZPM, which also results in Elizabeth Weir being captured by the Asurans. During the raid, McKay locates and activates the Wraith attack command in the Asurans' base code, causing them to launch their fleet against the Wraith. The Wraith attempt to use their computer virus again to deactivate the command, but McKay's modifications to the base code have rendered it ineffective. Meanwhile, the rebel Asurans use Weir's memories to create clones of the Atlantis team, but they are eventually tracked down and destroyed by Oberoth before they make any progress in their experiments.
In "The Seer", it is revealed that the Asurans have adopted a new strategy against the Wraith: depriving them of their food supply by annihilating human worlds. With hundreds of thousands dead, Atlantis is forced to ally with the Wraith to find a way to stop them. McKay eventually develops a plan to enhance the bond between the Replicator nanites, temporarily drawing them all together into a single mass that can then be imploded. Over Asuras, a combined fleet of Earth, Wraith, and Traveler ships engages the Asuran fleet, allowing time for McKay's plan to be successfully implemented. The highly dense Replicator mass sinks into the core of the planet, where the heat and pressure initiates fusion, resulting in an explosion that obliterates Asuras. At least one group of Asurans survive, led by Elizabeth Weir. This Weir is revealed to be the original in the season 5 episode "Ghost in the Machine", which depicts the ultimate fate of her group.
Being also composed of neutronium-based interconnected nanites, the Asurans have many characteristics in common with the human-form Replicators of Stargate SG-1, including resistance to damage, superior strength, and the ability to probe the mind of a human by extending their hand into the human's forehead. Their nanite nature also allows them to infiltrate through minute seams in solid objects. Although the Asurans are discrete individuals, their entire race is interconnected through a subspace link. This link allows the main body of the Asurans to "reset" the programming of a particular individual. A human can become infected by nanites through direct contact with an Asuran, after which the nanites use the body as raw material to replicate themselves until they achieve sufficient numbers to form an independent entity. In the process, they suppress the body's immune system and bond to the central nervous system, essentially engaging in a "battle of wills" with the host.
The Asuran base code is the collection of millions of commands that underlie Asuran behaviors, encoded in over three billion chemical base pair sequences. Amongst these directives are codes for aggression, for attacking the Wraith, against harming the Ancients, and against mimicking the appearance of known persons. Updates to the base code are disseminated periodically to all Asurans in a process known as a "merge". Rodney McKay of the Atlantis Expedition modifies the Asuran base code in "Progeny", "The Return", and "Lifeline", in the process inadvertently allowing the Asurans to override several of these directives. There is a central data core on Asuras that serves as a "back-up hard drive" for the base code. If destroyed, an Asuran's physical body can be reconstituted using data from the collective. Isolated Asuran nanites are vulnerable to an electromagnetic pulse, but in sufficient numbers they are able to assimilate organic components to protect themselves. The most effective weapon against individual Asurans is the Replicator disruptor, which disintegrates an Asuran by disrupting the link between its component nanites. However, the Asurans will eventually adapt and immunize themselves to the disruptor given enough exposure, and in "Lifeline" they take the strategy of repeatedly sacrificing their number to a Replicator disruptor field so as to gather the required data.
The Asurans emulate their creators, the Ancients, in appearance and lifestyle, and claim themselves to be the last of the Ancients. They are fueled by a rage that they cannot contain, written into their base code. Most Asurans are bitter towards the Ancients for rejecting them, believe them to be arrogant for disregarding their counsel during the war with the Wraith, and hate the humans of Earth for being the Ancients' favored children. They have little regard for human life and are unconcerned by the Wraith, claiming to have a long-term plan in the works for dealing with them.
The Asurans are one of the most advanced races within the Stargate fictional universe, as they possess all the knowledge of their creators, the Ancients, up to the point where they were abandoned by them. The Asurans have the ability to manufacture ZPMs, and utilize starships of Ancient design.
A small number of Asurans still admire and respect the Ancients, and wish to follow their creators' footsteps into Ascension. They are led by Niam, who believes that the aggression programmed into them by the Ancients is preventing them from Ascending. He asks Rodney McKay to remove this aspect of their base code, but even without it the other Asurans remain hostile and reset Niam's programming to fall in line with their beliefs. The remnants of Niam's group flee from the rest of their people and go into hiding. After McKay's meddling with their base code inadvertently removes the directives against mimicking real humans, these rebels create a replica of Atlantis populated by duplicates of the Atlantis Expedition, including copies of Jennifer Keller, Radek Zelenka, and Evan Lorne. They create organic copies of Sheppard, Teyla, Ronon, McKay, and Weir, in the hopes of learning the secret to Ascension. Each time the clones discover the deception, their memories are wiped and the experiment is restarted. However, Oberoth discovers the duplicate Atlantis and launches an attack on the city; Weir convinces Replicator Keller to let her and the other clones go before the city is destroyed.
In the episode "Ghost in the Machine", the last eight remaining members of Niam's group appear, led by the real Elizabeth Weir. Weir reveals that, after Asuras' destruction, she attempted to lead her group into Ascension, without success. One of their number, Koracen, proposed that they upload their minds into subspace, believing that they would then be free to move onto the higher places of existence. However, they find nothing there but noise and chaos, and eventually Weir arranges for them to return to nanite bodies using the technology on Atlantis. Ultimately, Weir realizes that they, as Replicators, are far too dangerous, and sacrifices herself to trick her group into following her through a space Stargate.
Niam, played by John O'Callaghan, is the leader of a faction of Asurans who believe that their goal should be Ascension. In "Progeny", Niam is solicitous to Elizabeth Weir and her team, unlike Oberoth. He convinces Oberoth to keep them alive, and he shows Weir their history and how the Ancients attempted to exterminate them. Niam asks the Atlantis team to remove their programming for aggression, and Dr. Rodney McKay takes advantage of this access to the Asuran base code to upload a "glitch" that freezes the Replicators, allowing his team to escape. Niam flees with the Atlanteans on a Puddle Jumper, but his treachery is discovered by his brethren and his programming is reset. He becomes hostile and the Atlantis team is forced to jettison him into space. His attack on Weir introduces nanites into her bloodstream, which eventually threaten her life.
In "The Return", after the Asurans overrun Atlantis, Sheppard and his team retrieve Niam's inert body from orbit in order to use him to access the Replicator base code and immobilize them. However, Niam unexpectedly awakens during the process, forcing McKay to disintegrate him with an Anti-Replicator Gun. Although Niam is gone, his followers continue to work towards Ascension in secret from the other Asurans.
Oberoth, played by David Ogden Stiers, is the leader of the Asurans and an enemy of the Atlantis Expedition. His first appearance is in "Progeny", where he informs Elizabeth Weir and her team that his people have no interest in an alliance against the Wraith. However, after he learns Weir and the others are from Atlantis, he has them imprisoned and interrogated, and orders the Asuran City Ship to attack Atlantis. Oberoth is aboard the City Ship when it self-destructs over Lantea.
In "First Strike", Oberoth has reconstituted his physical body from the Replicator collective. During the Asurans' attack on Atlantis, he answers Weir's call for negotiations. He informs her that due to the Earth battlecruiser Apollo's attack on Asuras, they now regard Atlantis as a threat to be destroyed. In "Lifeline", Oberoth confronts Weir on Asuras, during a mission to steal a ZPM for Atlantis. As she is being sustained by Replicator nanites, Weir makes contact with Oberoth and takes advantage of his overconfidence to fool him into thinking that her team has been captured. This buys Sheppard and the others enough time to complete their objective. Oberoth eventually overcomes Weir's control and captures her.
- Cetus (played by Panou). Second-in-command of the Asuran force that seizes Atlantis in "The Return". He is disintegrated when the Asurans activate the city's shield, as an Atlantis Expedition team had secretly modified the shield generators to emit a Replicator Disruptor wave.
- Koracen (played by Robert Moloney). One of Niam's dissidents, who joins Elizabeth Weir in seeking Ascension. In "Ghost in the Machine", he develops a way for his group to upload their minds into subspace. After returning to nanite form in Atlantis, he tries to escape rather than be transferred into a human body, and is destroyed by Weir.
- Lia (played by Leanne Adachi). One of Niam's dissidents, who joins Elizabeth Weir in seeking Ascension. In "Ghost in the Machine", she protests to John Sheppard that the rest of them knew nothing of Koracen's plans to escape and have abided by the terms set by the Atlantis Expedition. She and the others unknowingly follow Weir through a space Stargate at the end of the episode.
- Talus (played by David MacInnis). Leader of the Asuran force that seizes Atlantis in "The Return". His objective is to repair the city's stardrive and take it back to Asuras. He and the rest of the Replicators in the city are disintegrated when they activate the city's shield, as an Atlantis Expedition team had secretly modified the shield generators to emit a Replicator Disruptor wave.
In "Be All My Sins Remember'd", McKay and his team create their own human-form Replicator (played by Michelle Morgan) on Atlantis using the same equipment employed by the Ancients for the originals. She is designed to serve as the nucleus for McKay's plan to draw all the Asurans together into a single mass, and as such her programming is greatly reduced. Nevertheless, she quickly learns and develops a personality, and McKay names her "Fran" ("Friendly Replicator Android") after she requests a name. Fran is eager to fulfill her function as a weapon, and even assists McKay and Zelenka in improving their plan. On Asuras, she is beamed into the Replicator city and completes her mission. In "Ghost in the Machine", Elizabeth Weir downloads her mind from subspace into a Replicator body using Fran's template.
Based on data on the Asurans collected by the Atlantis Expedition, the scientist Richard Poole creates human-form Replicators on Earth under the guise of conducting research on using nanites for medical purposes. Poole is killed by one of his creations (played by Adrian Hein), who breaks out of the lab and attempts to obtain more neutronium with which to repair himself. His other Replicator creation, made in the image of the real woman Ava Dixon (played by Emma Lahana), enlists the help of John Sheppard in tracking down her counterpart. The hostile replicator is eventually beamed into space by the Apollo and burns up in reentry, while Ava's mind is downloaded into a virtual world to live out her life in peace.
- "Progeny" (Stargate Atlantis)
- "Reunion" (Stargate Atlantis)
- "The Return" (Stargate Atlantis)
- "First Strike" (Stargate Atlantis)
- "Lifeline" (Stargate Atlantis)
- "This Mortal Coil" (Stargate Atlantis)
- "The Seer" (Stargate Atlantis)
- "Be All My Sins Remember'd" (Stargate Atlantis)
- "The Real World" (Stargate Atlantis)
- "Hot Zone" (Stargate Atlantis)