The Asgard were once members of an ancient alliance with the Nox, the Furlings and the Ancients. The species was governed by the Asgard High Council, which monitored activity on protected worlds and formed decisions on actions taken against aggressors. Physiologically, the Asgard averaged about one meter in height, with grayish skin tones, small, skinny limbs, large heads and black eyes -- bearing a striking resemblance to the Roswell Greys described in countless UFO abduction stories. The Asgard were incapable of meiosis (sexual reproduction) for thousands of years. They resorted to a solely enhanced mitosis (cloning) existence, forcing them down a path that eventually led to their extinction. Before that time, some Asgard took drastic steps to ensure the survival of the species, including kidnapping people from Earth to study human development. Despite the Asgard's small physical stature, their size was no comparison to their intellect. They successfully developed a multitude of advanced technologies that dwarf those of the Goa'uld, including faster-than-light travel that can launch an Asgard vessel from one galaxy to another in minutes. The Asgard established a Protected Planets Treaty with the Goa'uld System Lords, keeping planets such as Cimmeria, Earth and K'Tau safe from direct invasion. But the Goa'uld Anubis's advanced technologies (taken or adapted from the Ancients) rivaled the Asgard's, allowing him to eventually ignore the treaty altogether and render it unofficially void. A chance encounter with Colonel Jack O'Neill of Earth forced the Asgard to reexamine humans and their role in the galaxy. They had studied human beings closely, determining that the species has great potential. However, O'Neill proved to them that humans were, in fact, ready to become a part of a bigger galactic picture, and the Asgard then designated him their representative from the human race. All of the Asgard's technologies and intellectual capabilities forced them to a deadlock in a battle with an artificial species in their galaxy: the Replicators. The Asgard, having exhausted all possible alternatives, greatly depended on the Tau'ri to render aid to the species in attempting to defeat this enemy. It was ultimately the efforts of humans that put an end to the chapter of the Replicators permanently when the machines entered the Milky Way to wage war with the Goa'uld. Through the potential of Jack O'Neill, the Asgard acknowledged that they considered humanity to be the fifth race. When their genetic degradation led to a point where their last attempt to halt it brought about a debilitating disease, they chose to put this to the test. Before retreating to their planet, the Asgard endowed the Earth vessel Odyssey with a library computer containing the sum of their knowledge and technology. To prevent the rest of their technology from falling into the wrong hands, they detonated Orilla's core, completely eradicating the Asgard footprint from the universe -- or so it was believed.
More than a year later a splinter group of Asgard, who had broken off to solve their genetic degradation problem using less ethical means, were discovered in the Pegasus Galaxy. They were not surprised when they learned of the death of their brothers in the Othalla Galaxy, which seemed to only strengthen their resolve to fix their cloning problem by any means necessary.