Sozin's dragon

Sozin's dragon is the blue dragon that Fire Lord Sozin used as a mount. It is presumed that Sozin's relationship with the dragon was much like Roku's relationship with Fang, though it is also possible he enslaved it, it was only a pet, or it was only a beast-of-burden. Sozin is the only Fire Lord known to have a dragon. As vicious as his master, Sozin's dragon was able to fly over great distances at very fast speeds.

Not much is known about the dragon's history or when Sozin got it. It may have been between the 25 years Sozin and Roku did not see each other. It is possible that this Dragon was killed when Sozin started the tradition of hunting dragons for glory. It is also possible that the dragon died when its master died.