Trevean was a native of the Gamma Quadrant planet Teplan in the Teplan system which was infected with the Blight by the Jem'Hadar. Trevean, who had lived with the Blight longer than anyone there, had taken on himself the task of easing his people's suffering by giving toxic herbs to those who had 'quickened'.
He was opposed to the "false hope" Doctor Julian Bashir offered, and encouraged his patients to commit suicide rather than permit themselves to be experimented on. After Bashir's first attempt at a cure failed, causing his patients to suffer horrible and painful death, Trevean showed up to put the remaining patients out of their misery. But when it was discovered that Bashir's antigen cured the unborn, he was eager to learn how to manufacture and distribute it to pregnant women, so that the next generation of Teplans may be free of the disease. (DS9: "The Quickening")