The Koan are humanoid in shape but are drastically different; possessing numerous spines on their head which serve as sensory organs. As part of their mutations, they have become a nocturnal species possessing a far better night sight allowing them to navigate in dark caverns. The genetic changes have also affected their minds which have degraded their minds to the point of being almost animalistic in their actions. (SGA: "Reliquary")
The Koan were once a Human species that developed a civilization during the time of the Ancient's reign within the galaxy. They were in contact with the Ancients during the time of the rise of the Wraith when they began suffering from attacks from the vampiric race. In desperation, the Koan turned to the Ancients for help but received none. Lacking advanced technology, the Koan's leading geneticist, Dorane, turned to bio-weaponry to drive off their enemies.
This succeeded and the Wraith departed from their world, however, the same bio-weaponry affected the Koan themselves. Many were killed while others were mutated into a more monstrous inhuman form. Dorane made a plea to the Ancients to help him and his people but they spurned his actions. As such, Dorane took matters into his own hands.
Dorane and the remaining Koan would relocate to a planet inhabited by the Thesians who were building a great city in conjunction with the Ancients who had stored a Repository on the world. Dorane would claim to be an Ancient from Atlantis that had arrived to help the Thesians construct their city. In reality, he would conduct experimentation on the Thesians in order to reverse the damage done to the Koan but this would fail when the Ancients retaliated. The Koans were forced into stasis by Dorane until a new opportunity emerged.
The Koan would aid their master, due to mind control technology, to attack Atlantis however this would be foiled by Major John Sheppard. The remaining Koan were relocated back to their homeworld. Unfortunately, any further attempts at reversing their mutation would further deteriorate their condition. (SGA: "Reliquary")