The Asurans are a race of sapient machines in the Stargate universe.
The Asurans are made of trillions of nanites. They were created during the Ancient-Wraith War as a weapon to destroy the Wraith. The nanites eventuallly became more complex and imitated the form of their creators (the Ancients). They can walk through walls, regenerate themselves, and are impervious to most energy and projectile weapons.
The Asurans were an experiment by the Ancients to design a new weapon to fight the Wraith. They appealed to the Ancients several times to remove the programmed aggression in them. Some time later, the Ancients sent a fleet of ships to destroy the Asurans. A few nanites survived and began rebuilding.
10,000 years later, the Atlantis Expedition encountered the Asurans. The Asurans found out Atlantis wasn't destroyed by the Wraith and sent their city-ship to attack Atlantis. The Atlantis-1 team managed to escape the city-ship after setting the self-destruct. A few weeks later the Asurans captured Atlantis, but the Atlantis-1 team, Weir, and Beckett managed to retake the city just as the Daedalus arrived to nuke the city.
Over the next two months, the Asurans were building a fleet of ships to attack Earth. The IOA sent the Apollo to use the Horizon to destroy the ships and shipyards. The attack was successful; however, several hours later the Asurans managed to repair their shipyards and cities. They sent a satellite ship with a stargate to attack Atlantis. The gate activated and a beam was fired through at Atlantis. The Atlantis Expedition decided to leave Lantea to go to M12-578. The beam grazed Atlantis' main tower and caused quite a bit of damage to Atlantis itself.
A few hours later the Atl-1 team went to M2R-227 to steal a ZPM, but they also decided to activate the base code of the Asurans. The Asurans began attacking the Wraith several hours after Atlantis reached M35-117. Over the next few months, the Asurans built more ships and began targetting human worlds to destroy the Wraith's food supply. The Apollo and Daedalus were sent to Atlantis after being upgraded with the new Asgard technology acquired from the Asgard database. The Atlantis Expedition made an alliance with the Wraith and Travelers to attack the Asurans. The attack was successful and the Asurans were destroyed.
The Asurans follow the Ancients in government and are ruled by a governing council.
The Asurans have good production capacity, being able to build nineteen ships in two months. The Asurans are immune to most energy and projectile weapons. The ability to walk through walls means most conventional physical barriers are useless. They are a genuine threat to most powers that encounter them.