Thunder Dragons are the masters of electricity. Their wings gather energy as they soar through the clouds, and when they clap their wings together they can create devastating arcs of lightning. They can stay airborne nearly indefinitely, landing only to sleep and breed; they catch their prey from the air and take moisture from the clouds. A thunder dragon’s roar is considered to be an omen of misfortune.

Dragons are highly-intelligent reptilian creatures that—from a human perspective, at least—appear to live forever. Many different varieties of dragon exist, each with their own unique qualities, habitats, and behavior. Adolescence in dragons is usually marked by the growth of a hatchling’s wings, although not all breeds of dragons grow wings and some breeds have other traits that indicate the beginning of maturation. In Galsreim, dragons and humans coexist peacefully.

Fillmore enjoys making "musical stuff", which usually means playing and singing, helping other dragons figure out their musical style, or setting up a show for himself or others. He does not use his lightning abilities to destroy, except an instrument after a particularly energizing performance. Rather, he uses them to light up a venue, and he hopes one day he can figure out how to build and power sound-producing and sound-amplifying devices with electricity. Fillmore's territory is a single stone structure where musicians and spectators are invited to visit. Some people visit his "cave" only to look at the colorful artwork posted inside, and that's okay with him.