Vash's primary goal was not to gain knowledge about ancient cultures, but to sell their artifacts for a profit. To this end, she frequently used methods that were considered unscrupulous by the scientific community, including visiting many archaeological sites that were barred to outsiders such as Sarthong V. (TNG: "Captain's Holiday")
Her shady ethics, and consistent sale of priceless artifacts, twice got her membership suspended from the Daystrom Institute Archaeological Council. Her professional choices were also the reason she was not welcome on several worlds. Vash was banned from the Royal Museum of Epsilon Hydra VII, was a persona non grata on Betazed and had a "dead or alive" (preferably dead) warrant issued for her on Myrmidon because she had stolen the Crown of the First Mother. Though Professor Woo would offer her reinstatement to the Council and a lecture position at the Daystrom Institute in 2369, Vash made it clear that between knowledge and profit, she would choose profit every time. (TNG: "Qpid"; DS9: "Q-Less")
For five years in the middle of her career, until approximately 2366, Vash worked as the personal assistant to Dr. Samuel Estragon while he devoted his life to searching for the legendary Tox Uthat. After his death in the 2360s, Vash continued the search using his notes and ultimately found the Tox Uthat in 2366 on the planet Risa where it had been hidden by its creator. (TNG: "Captain's Holiday")
Romance with Jean-Luc Picard
It was on Risa that Vash also met Captain Jean-Luc Picard, himself on shore leave from the USS Enterprise-D. After initial conflict the two found themselves kindred spirits of a sort and began a romantic relationship.
Vash took advantage of Picard's presence to distract and foil Sovak, a Ferengi, who had occasionally been employed by Estragon for certain purposes – not always legitimate ones. Sovak was determined to recover the Tox Uthat for himself in order to sell it, in addition to being infatuated with Vash. Unknown to Sovak, and for a time to Picard, Vash had uncovered the Uthat before either of them had arrived. Picard eventually discovered the deception and was instrumental in the ultimate fate of the Uthat.
A year later Vash reappeared in Picard's life when she attended the annual Federation Archaeology Council symposium hosted by the USS Enterprise in orbit of Tagus III. Her unannounced visit surprised Picard, who greeted her warmly. However, the warmth between them faded slightly when Vash found that Picard had never mentioned her to his colleagues after meeting her on Risa.
Picard visited her quarters to give her an explanation, but their reconciliation was side-tracked when he discovered archaeological equipment and a map of the Taguan ruins, which she wanted to explore. The ruins had been off-limits for non-Taguans for the past one hundred years and the realization that Vash intended to explore them illegally while a guest of the Enterprise angered Picard.
At the same time, the entity Q appeared on the Enterprise claiming he wanted to settle a debt to Picard, who had protected Q on a previous occasion when he had been stripped of his powers by the Q Continuum. Picard resisted Q's attempts to "do something nice" for him, but when Q discovered Picard's relationship with Vash he took matters into his own hands.
Q staged a Robin Hood fantasy in which Picard was forced to choose between rescuing Vash, herself forced to play the part of Maid Marian, or letting her die at the hands of Sir Guy of Gisbourne. Picard was ultimately successful in his rescue, and the fleeting bitterness of their earlier reunion faded as the two rekindled their affection for each other. (TNG: "Qpid")
Partnership with Q
During the course of the drama in Sherwood Forest, Q became fascinated by Vash, finding her full of deceit and duplicity. Genuinely curious about her, Q offered Vash a chance to accompany him exploring the universe. Though Picard warned her against accepting the offer, she agreed and after Picard demanded Q guarantee her safety as payment of his debt. Vash kissed Picard goodbye and left the Enterprise with Q. (TNG: "Qpid")
For the next two years Vash and Q explored some of the most splendid archaeological sites in the galaxy. They visited numerous sites that no Human had ever seen before, including Errikang VII, Brax, and Erabus Prime where Vash was almost infected by a local insect though she was saved by Q's intervention.
In 2369, Vash broke off her partnership with Q while in the Gamma Quadrant and was found by Jadzia Dax and Pauley a short time later and returned to Federation space with the USS Ganges. When she arrived at Deep Space 9, she did not come empty-handed. One of those artifacts was a crystal with a high molecular refraction index that resembled Promethean quartz and converted the runabout's power sources into gravitons. Power levels of the runabout were nearly zero, life support was down and they barely reached the station where they were rescued by Miles O'Brien and Dr. Julian Bashir.
In order to sell the artifacts she had brought back with her, she partnered with Quark. Quark found a kindred spirit in Vash, who expertly manipulated him with her feminine charms and an ear massage. Quark arranged an auction for some noted Gamma Quadrant artifacts, including a Verathan statue, assorted gems, a gold necklace, and an exceptional gold dagger. However, the crystal's presence on the station resulted in focused graviton pulses, causing random hull breaches. The resulting graviton field even moved the station towards the wormhole, bringing it into grave danger. Fortunately, Lieutenant Dax, Commander Sisko, and Major Kira tracked down the problem and beamed the crystal into space. There it turned out that the crystal was an embryonic lifeform, which now could return to the Gamma quadrant.
Vash's presence on Deep Space 9 did not go unnoticed by Dr. Bashir who made advances towards her; nor by her former partner, Q. Q attempted to lure her back to him by enticing her with the possibility of more adventures to exotic locales such as the Teleris Cluster, the Lantar Nebula, and Vadris III. She turned down Q's repeated entreaties, much to his disappointment; though she did seem to retain some level of partiality to the entity. Vash briefly considered becoming a lecturer at the Daystrom Institute, which was interested in her because of her time spent in the largely still unexplored Gamma Quadrant. However, she was convinced by Quark to continue her journeys, with him as a backer and business partner. Quark kissed her affectionately on the hand as they walked away discussing their plans. (DS9: "Q-Less")
"Look, I don't mean to appear rude, but I am not seeking jamaharon."
"All right. But you really should try it some time."
"If I "try it", it will be at a time of my own choosing."
"That's fine with me. It's not as though I was offering to help you find it."
- - Picard and Vash soon after meeting on Risa
"You mean you came alone?"
"Yes, now let's..."
"What kind of plan is that?"
"An excellent one if you'd only hurry up."
- - Vash and Picard during his rescue attempt in Nottingham Castle
Vash was played by Jennifer Hetrick.
Vash was named after Susan Vash, a casting director whom Ira Steven Behr worked with on the television series Once a Hero. (Star Trek: The Next Generation Companion) Her name was changed into "Viriad" in the French version, because "Vash" sounds like the French word vache, which means cow. According to the script for "Captain's Holiday", Vash's name was pronounced as "VASH". 
Vash was created in an effort to introduce an independent female character who could be written as a romantic interest of Captain Picard. Stated Ira Steven Behr, "People might not realize this, but even Vash was an attempt to bring in a ballsy woman who's not your typical Star Trek woman, a clear thinker both in terms of what she did in her own life and sex and the whole bit." (Captains' Logs Supplemental - The Unauthorized Guide to the New Trek Voyages, p. 17)
Recalling how she adapted to the part of Vash for "Captain's Holiday", Jennifer Hetrick said, "I just used my own imagination and what I know of myself and found her very adventurous and conniving to a degree, but also vulnerable and committed." (Captains' Logs: The Unauthorized Complete Trek Voyages, p. 195)
Following her appearance in "Q-Less", Ira Steven Behr considered bringing Vash back to Star Trek: Deep Space Nine. Shortly after the sixth season of the show began, he commented, "I'd like to see her back but so far inspiration has not struck." (AOL chat, 1997)
Vash is a major character in the Star Trek: Deep Space Nine - Millennium novels. In the first book in the series, she is responsible for the discovery of the Red Orbs, an action that (in an alternate future) led to the destruction of Deep Space 9. In that future, she subsequently accompanied an elderly Picard, now crippled by Irumodic Syndrome, and an older Nog into the past, where the three of them became fabled figures in Bajoran mythology, and wrote 'prophecies' that detailed the events of that timeline up to the point where they left it. It was also hinted here that she regards Picard as her 'best love', although she briefly displays an attraction for Jake Sisko and Julian Bashir as well.