Sulan was the chief surgeon of the Vidiian Sodality, who operated from the hidden Vidiian base on Avery III. In 2371, the USS Voyager was surveying the Avery system when Lieutenants B'Elanna Torres, Tom Paris and Pete Durst were captured by the Vidiians.
Sulan believed that Torres' Klingon DNA was resistant to the phage. To obtain a pure test subject, he split her into two individuals – one completely Human, the other Klingon – using a genotron, and then infected the Klingon Torres with the phage. Sulan was gratified that Torres' Klingon physiology appeared to be successfully resisting the phage. He came to greatly admire the Klingons, telling Torres that they were the "most impressive species" he'd ever seen.
The Klingon Torres flirted with Sulan in order to persuade him to set her free. After Durst was killed for his organs, Sulan grafted his face over his own in hopes of winning her affection, but Torres was disgusted and horrified. Her anger helped her to break the bonds, and she attacked Sulan and escaped from the lab. Just as she and her Human half were about to beam back up to the ship, Sulan fired and the Klingon Torres jumped in front of the beam to save her Human self, dying in the process. His research was never completed. (VOY: "Faces")