Laolith

One of a number of dragons summoned by Liessa at the Wyrmberg, but the only one that she personally rode. Despite a strict edict that there were to be no unaccompanied flights, Laolith flew and hunted a pig because he was hungry. She tempted him with horses and a wizard, but he commented that after eating one wizard, half an hour later you needed to eat another one... She flew him in pursuit of Hrun the Barbarian twice- first to capture him, and second to hunt him down after Twoflower and Rincewind "rescued" him from her custody.

Like all the dragons of the Wyrmberg, he only appeared if someone truly believed in Noble dragons, and even then, the believer had to be in an intense magical field, powerful enough to pull a dragon into the world. So, if Laolith left the magical field of the Wyrmberg, he would get more and more transparent, and then vanish.