Gelidon

 is a dragon. As an NPC, is played by Matthew Mercer.

Appearance
Gelidon is "of hoarfrost color"; in other words, a white dragon.

In the Vellum Steeple Archives, Beau read a book that spoke of a cursed location to the far eastnortheast of Uthodurn, known as Mythburrow, about 350 miles away. It talked of an ancient dragon of hoarfrost color and quaking roar that was thought to possibly nest there, but unseen in nearly a century. The dragon’s name is Gelidon, the Nightmare in Ivory.