Professor Samuel Estragon was a scientist that devoted half of his life to locating the Tox Uthat, a kind of quantum phase inhibitor invented by Kal Dano in the 27th century. It was a palm-sized crystal capable of stopping nuclear fusion within a star.
Shortly before his death in 2366, Estragon uncovered new evidence of the artifact's location on Risa and encoded his research notes and maps on a data disk. After he died, Vash used his notes to locate the artifact, and used Sovak to finance her trip there. Sovak and two Vorgon felons from the 27th century also tried to obtain the device. Captain Picard, vacationing on Risa, became involved and eventually destroyed it to make sure no one could do harm with it. (TNG: "Captain's Holiday")