A Delta Quadrant species whose economy rests on exporting deadly theta radiation waste, dumping it on other peoples' territory instead of cleaning it up.
The Malon are a humanoid species from the Delta Quadrant whose society is built around heavy industry. Their production creates enormous quantities of theta radiation waste, and the Malon export it to remote regions of space using huge freighters, poisoning whatever lies there. Exposure to the radiation causes horrific injuries.
Voyager first meets them in the episode Night while crossing a vast starless void. The ship discovers that the region's inhabitants are being killed by Malon dumping, led by a trader named Emck, who offers Voyager a way out of the void in return for its cooperation. Kathryn Janeway refuses and instead destroys the vortex the Malon use to enter the area. The species returns in Juggernaut, where a damaged Malon freighter carrying theta waste threatens to explode, and B'Elanna Torres helps a rescue team stop it while confronting a mutated Malon crewman.
The Malon serve as a pointed commentary on pollution, showing a society that has chosen profit and comfort over the safe treatment of its waste.