Sulan was the Vidiian surgeon who split B'Elanna Torres into separate Klingon and human beings in search of a cure for the Phage.
Sulan was a chief surgeon among the Vidiians, a species devastated by the Phage. He believed that Klingons' natural resistance to the disease might hold the key to a cure, and he used captured prisoners as subjects in his research.
In Faces, Sulan separated the half-Klingon B'Elanna Torres into a full Klingon and a full human, infecting the Klingon with the Phage to study her. Infatuated with his subject, he murdered crewman Peter Durst and wore his face to win her favor. His plans collapsed when the two versions of Torres worked together and Voyager rescued its people, leaving his research in ruins.