The society of the Gadmeer was a peaceful and technologically advanced one that lasted for over 10,000 years. Over a thousand years ago they were defeated by a superior power due to a lack of military technology and tactics, and thus their race apparently died out. To prevent their culture from vanishing they built a giant vessel which stored all their knowledge, including arts, mathematics and even the DNA samples of thousands of the plants and animals of their homeworld.
This ship then searched for another world which would be similar to their original homeworld and over time it scanned many millions of planets. Ultimately it found a world called P5S-381 by Stargate Command, on which it performed a terraforming-like process so that the Gadmeer civilization could be reborn. It however turned out that the SGC had recently settled the Enkarans on this planet, which was the only known world reachable by Stargate on which the Enkarans could survive. SG-1 was faced with the terrible choice of either destroying any hope of the Gadmeer's return or robbing the Enkarans of a home again. Eventually, Daniel Jackson worked with the terraformer's caretaker to locate the original Enkaran home world, which had no Stargate. The caretaker agreed to bring the Enkarans home in the terraformer, before returning to the now-uninhabited planet to complete its work. (SG1: "Scorched Earth")
Very little is known about Gadmeer technology but it appears to be quite advanced, but whether it's as advanced as the technology of either the Asgard, Nox, or Furlings is unknown but quite possible (with Ancient technology being far more advanced).
- The Gadmeer look oddly like the Pokémon Mewtwo or the Aliens from Independence Day, although it's doubtful whether this was intended as a deliberate reference.
- Unlike humans, who are carbon-based, the Gadmeer are a sulfur-based lifeform.