There was once an alliance that was built over many millennia, of four great races of the galaxy: the Asgard, the Nox, the Furlings, and the Ancients. The Asgard believed that humans had already taken the first steps towards becoming the Fifth Race.
As the Asgard faced their demise, they took steps to preserve their legacy. Although not all on the High Council agreed, many among the Asgard, including Thor, felt that the Tauri had earned their respect and friendship, and that the hope of preserving the future lay with the humans of Earth. The Asgard installed all their knowledge and technology aboard the Odyssey and bequeathed their legacy to those they considered the Fifth Race.