From the introduction:
Essentially all of Level 10 is the lair of a dragon named Bargelos. A descendant of Metterak, Bargelos came to Dragon’s Delve to follow in the Dragon Prince’s footsteps and reclaim his legacy. He never made it deeper than Level 10, however. There, he faced the sorcerer, Theophrastus. The two battled to a standstill, the sorcerer inflicting a few grievous, lasting wounds on the dragon. However, Theophrastus knew that he would never beat the dragon, and thought of a way to possibly outlive him. So Theophrastus sealed himself in a magical gem on Level 8 so that he could sleep for 1000 years. That was 480 years ago. Bargelos, although much older and more powerful now, still has an unnatural fear of the sorcerer. If fact, the dragon has only become more and more paranoid and fearful. Although he possesses the means to break the sorcerer’s prison, he fears to use it himself.