Kasper Jordan was a former Corporal in the US Army, as part of Unit 91, an experimental formation that was designed to produce psychic soldiers. After a successful experiment on base in Germany, Jordan developed the abilty to make himself invisible to others when required. This ability however, had a serious effect on his brain power and depleted it's electricity, making him more and more ill and weakening his invisibility.
Jordan travelled back to the United States and began tracking down old enemies and killing them, believing himself to be a retributer. After a killing spree that left him reeling, he was hunted and found by the FBI, with Fox Mulder discovering his hideout. Before Jordan could turn his ability on Mulder, however, he suffered a brain aneurism and died at the scene. He was denied a Military burial. ("Flicker")