Dejaren was an HD25 Isomorphic Projection with extreme hazard clearance, serving aboard a Serosian vessel in 2374. His responsibilities there included cleaning the reactor core and ejecting antimatter waste.
In early 2374 his isolation led to his program destabilizing. Having become obsessed with cleanliness to the point of psychosis, he killed the crew and sent a distress call. This was answered by the USS Voyager, and both The Doctor and B'Elanna Torres beamed to the ship.