Nelson was a Human member of the Maquis, a former compatriot of Chakotay and B'Elanna Torres who was slaughtered by the Dominion-reinforced Cardassians in 2374. (VOY: "Hunters")
The day after Torres learned the news that all of her Maquis friends were dead, she created the holodeck program "Torres Zeta-1" in which Nelson was slaughtered along with three other of her Maquis buddies, Sahreen, Li-Paz and Meyer. The purpose behind this was in order to "feel something," as she otherwise felt nothing at all viewing their dead corpses. (VOY: "Extreme Risk")
Nelson was played by background actor Gavin Chase who received no credit for this appearance.