They are characterized by small ridges on their chin and two horizontal ridges just above their nose. The ridges on the Vaadwaurs' faces give them very sharp features. A large fin-like crest runs across the center of their foreheads, becoming wider as it reaches the top of their skulls. Their hair grows from around the mid-region of their skull, just where their fin ridge seems to end. Neck ridges extend from their ears, down along their neck and onto their shoulders where they curl in towards the center of their chest. This gives the neck ridges a cobra-like appearance overall, somewhat similar to Cardassians.
Prior to the 15th century, the Vaadwaur discovered and mapped the Underspace, a vast network of subspace corridors that allowed them access to star systems throughout the Delta Quadrant. They used the Underspace for exploration, commerce, and conquest, earning them the envy and enmity of hundreds of species. The population of the Vaadwaur around that time was six billion.
The Vaadwaur encountered the Borg during their travels, who at the time had assimilated only a handful of star systems. Another of the races they encountered were the Talax-ilzay, the ancestors of modern Talaxians, whose folklore included stories of a "phantom army" that appeared out of thin air and destroyed entire colonies before disappearing. In the old Talaxian language, "vaadwaur" is a word that means "foolish", an admonishment to those who trusted the Vaadwaur. Numerous other, similar references also testify to the aggression of the Vaadwaur.
Eventually, a coalition comprising the Turei and other species was formed to end the Vaadwaur threat once and for all. Their campaign culminated in the orbital bombardment of the Vaadwaur homeworld in 1484, which was believed to have resulted in the extinction of the Vaadwaur. The Turei subsequently claimed the Underspace for themselves.
A Vaadwaur battalion, numbering six hundred, managed to survive the attack underground in stasis units. Believing that the Turei coalition would quickly disintegrate after their defeat, they intended to reawaken in five years and reclaim one of their former colonies. However, a technical malfunction left them in stasis until they were discovered by the crew of the USS Voyager, 892 years later in 2376. The Voyager crew found the Vaadwaur a new planet on which to rebuild.
Frustrated by their antiquated technology and the encroachment of successors such as the Borg and the Devore Imperium on their former holdings, the Vaadwaur resolved to take control of Voyager instead. They were driven back with help from the Turei and Gedrin, one of their own who disagreed with their imperialistic ambitions. Fifty-three Vaadwaur vessels managed to flee into the Underspace, disappearing to parts unknown.
The Vaadwaur were not seen for a number of years, until revealing themselves in 2387, in The Round Table, the area of Operations for Bravo Fleet's Task Force 38 by the Mordred Nebula. The Washinton was the first to detect the Vaadwaur coming in and out of underspace near the the Nebula. It was then resolved for the Washington to continue to observe whilst the Excelsior was ordered into the region, not only as a show of force, but to find out exactly what the Vaadwaur are up to.