Vaadwaur were characterized by small ridges on their chins and two horizontal ridges just above their noses. The ridges on the Vaadwaurs' faces gave them very sharp features. A large fin-like crest ran across the center of their foreheads, becoming wider as it reached the tops of their skulls. Their hair grew from around the mid-region of their skulls, just where their fin ridges seemed to end. Neck ridges extended from their ears, down along their necks, and onto their shoulders where they curled in towards the centers of their chests. This gave 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" was a word meaning "foolish", appearing in several tales in Eldaxon's Collected Folklore featuring death and evil.
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. (VOY: "Friendship One")
In 2376, when Voyager was forced to land on the Vaadwaur homeworld to escape the Turei after they accidentally 'intruded' into a subspace corridor and the Turei insisted that they be allowed to board to wipe Voyager's records of the trip. Having revived Gedrin after discovering his chamber, the Voyager crew awoke a large number of Vaadwaur and worked to find 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, who had come to disagree with their imperialistic ambitions after spending time with the crew. Fifty-three Vaadwaur vessels managed to flee into the Underspace, disappearing to parts unknown. (VOY: "Dragon's Teeth")
In the original script for "Dragon's Teeth", the Vaadwaur went into hibernation for five hundred years. It would have made it more logical for their history to be nearly forgotten in Borg and Talaxian histories. (Star Trek: Voyager Companion (p. 331))
Though the Vaadwaur were not seen directly again by either Voyager or any other Federation or Delta Quadrant ships, Dr. Julian Bashir identified them as a threat to the Federation a few months after "Dragon's Teeth" and "Pathfinder" after examining the Pathfinder Project database in the Star Trek: Deep Space Nine Section 31 novel Abyss.
The Vaadwaur appear as a major antagonist in the Delta Rising expansion of Star Trek Online. Set roughly three decades after the events of Voyager, the Vaadwaur, using advanced technology provided by the Iconians, have become a powerful military force known as the Vaadwaur Supremacy, intent on conquering the Delta Quadrant. The Vaadwaur nearly exterminate the Krenim, lay siege to Kobali Prime, homeworld of the Kobali, and come into conflict with the Delta Alliance, a coalition of Alpha and Beta quadrant powers (including the Federation, Klingon Empire, and Romulan Republic).