Lenara Kahn in 2372.
Lenara Kahn (played by Susanna Thompson) was a joined Trill scientist (with the Kahn symbiont) at the Trill Science Ministry. In 2372, she and her colleages, Hanor Pren and her brother Bejal Otner, visited Deep Space 9 to conduct field tests on a technique to create artificial wormholes. Although initial results were promising, it was found that the wormhole was unstable.
While on the station, Lenara became acquainted with Jadzia Dax. Their former hosts, Torias Dax and Nilani Kahn, had been married, and they found their past feelings for each other re-emerging. After Lenara was nearly killed on the accident aboard the USS Defiant, Jadzia voiced her willingness to resume their previous relationship, despite the cost of reassociation. However, Lenara was unwilling to accept exile from Trill society, and the two parted company. (DS9: "Rejoined")
By 2373, Kahn had developed a way to seal the wormhole without damaging it or harming the beings living within, using a series of phase-conjugate graviton beams. The technique was put into practice later that year, as a Jem'Hadar fleet was approaching the Bajoran wormhole, about to invade the Alpha Quadrant. The attempt was sabotaged by a Changeling infiltrator, disguised as Julian Bashir. The modified beam made the wormhole unable to be collapsed, allowing more Dominion ships throught it. (DS9: "In Purgatory's Shadow")