Doctor 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 is a palm-sized crystal capable of stopping nuclear fusion within a star.
After his death in 2366, his assistant Vash carried on and succeeded in locating the Uthat. Sovak, a Ferengi entrepreneur who sometimes worked with Estragon on less-than-ethical archaeological expeditions, had paid Vash to steal Estragon's notes on the location of the Tox Uthat. Vash used Sovak's money to conduct her own search for the fabled object, with Sovak trailing her. 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 the Tox Uthat to make sure no one could do harm with it. (TNG: "Captain's Holiday")