Thelhen is a keeper of Dalish clan Virnehn.
Involvement
After Gaspard de Chalons has trapped Celene, Briala, and their companions in Halamshiral, the group decide to join forces and seek aid from the Dalish. When Briala and her companions finally reach the Dalish clan of Virnehn, its keeper Thelhen makes it clear that his clan wants nothing to do with Briala's companions or their plans, nor do they care about the city elves whom they do not consider to be elves at all (they call them "flat-ears"). He believes that even if they help Celene defeat Gaspard in exchange for the Dales, they would only face a similar betrayal like when the Chantry declared an Exalted March on the elves centuries ago.
The clan say they are only interested in reclaiming their past, going to such lengths as to summon a demon, Imshael, to interrogate it so that it can help reactivate the Eluvian network.
Imshael created a Keystone that would lead whoever wielded it through a series of Eluvians that would end in a central chamber connected to all of the Eluvians in Thedas. From there, whomever holds the Keystone could reactivate the Eluvians and reset the spoken password needed to travel through them.
Imshael offered the Keystone to the clan's keeper, Thelhen, in exchange for a body to posses. Thelhen refused and imprisoned the spirit indefinitely in a stone circle prison. Imshael then tricked Empress Celene's champion, Ser Michel de Chevin , into freeing it.
Thelhen along with most of his clan were massacred by the demon after Michel unwittingly frees Imshael.