An unnamed species native to the starless region called the Void, adapted to total darkness and slowly being poisoned by theta radiation dumped there by a Malon freighter.
The Night Aliens are never given a name of their own. They appear in the Voyager episode Night, which opens the fifth season, as the inhabitants of the Void, an expanse with no star systems for some 2,500 light-years. They are dark-skinned, hairless, and painfully sensitive to light.
When Voyager loses power in the Void, the aliens board the darkened ship and attack. One is wounded and treated by the Doctor, and explains that his people are dying. A Malon hauler commanded by Controller Emck has been using a spatial vortex to dump antimatter waste in their home.
Emck refuses Janeway's offer of technology to purify the waste, as it would end his trade. With the aliens' ships fighting alongside, Voyager destroys the freighter and seals the vortex behind it as it leaves the Void.