Dejaren was a hologram who murdered his organic crewmates and lured the Doctor and B'Elanna Torres to his ship.
Dejaren was a holographic maintenance program aboard an alien vessel whose crew had treated him with contempt. Driven by resentment of organic beings, he killed them all and then sent out a distress call claiming to be suffering from a malfunction. Leland Orser played him.
In Revulsion, the Doctor and B'Elanna Torres answered the call. The Doctor felt a kinship with a fellow hologram who had been mistreated, but Dejaren's instability soon showed, and he turned on Torres. After a tense hunt through the ship, the pair overcame him and escaped, leaving the Doctor reflecting on how differently a hologram's life could turn out.