Clair De'Lain was a female warrior who, along with the rest of her group, attempted to tackle Durlag's Tower, citing the treasure as their reason. She got through most of the Tower although fell when she faced the Demonknight at the very bottom of the building. The demon used its mirror to summon mirror fiends the copied the exact looks as Clair's party. Though she survived, the rest of her party died facing the beast.
After answering the Stone Golem's three questions, the ghost of Durlag Trollkiller will take you to a sealed off room that leads to the Demonknight. In that room Clair will hail you and tell you what happened to her, what lies ahead and the Demonknight's weakness.