Sozin's dragon was a blue dragon that Fire LordSozin used as a mount and his animal companion. As vicious as his master, Sozin's dragon was able to fly over great distances at very fast speeds. Sozin was the only Fire Lord known to have a dragon.
In 12 BSC, Sozin used his dragon to cross the hundred miles that separated the Fire Nation Capital and Roku's island in order to help his old friend battle the erupting volcanoes that threatened to engulf the island in fire. When Roku was fainting from the poisonous volcanic gases, Sozin's dragon swooped in and saved only his master, while the pyroclastic flow swept over the Avatar and killed him.