Doctor Rislan was a Nyrian astrophysicist who was second in command to Dammar. He was from the colony on Nyria III.
In 2373, Dammar led a plot to kidnap the crew of the USS Voyager and hijack their starship. He did this by translocating a crew member to a habitat on a Nyrian biosphere vessel and beaming a Nyrian onto the ship to replace the crew member.
When Rislan was transported to the ship he pretended he did not know what was happening, and offered to help B'Elanna Torres find a solution. This helped him gain access to the engine room. Torres conducted a tetryon scan of the area against the scientist's objections. In order to stop her from discovering the truth, Rislan struck a security officer, stole his phaser, and transported Torres to the vessel.
After the crew was able to gain access to the translocator, Rislan and Dammar were relocated to an arctic-like environment and, not able to withstand the cold, surrendered. (VOY: "Displaced")