In 2373, Adin, Tieran, and a female named Nori were beamed aboard the USS Voyager just before their ship exploded. The Doctor and Kes were unable to save Tieran, who died of his injuries, but not before he transferred his consciousness into Kes.
Kes/Tieran became paranoid due to the stress of the mental conflict between their minds. Adin tried to convince Tieran to break control over Kes and transfer to a new host. He was fearful that there would be irreversible damage done to his mind if he did not. Tieran ended up killing Adin using Kes' mental abilities. (VOY: "Warlord")