Demmas was the eldest son of the Ilari Autarch, who explained to Janeway that Kes had been possessed by the ancient tyrant Tieran.
Demmas was the oldest son of the Autarch, the hereditary ruler of the Ilari. His family had overthrown Tieran two centuries earlier, never knowing that the tyrant had survived by passing from host to host.
In Warlord, Demmas met Janeway after Kes, possessed by Tieran, killed an Ilari representative and fled. He revealed Tieran's history and joined forces with Voyager. Tieran murdered the Autarch and tried to turn Demmas's younger brother Ameron against him, but Voyager's crew freed Kes and ended Tieran's reign.