In the Dark Sun D&D setting, Borys is the name of the first Athasian dragon who was the Sorcerer-King of Ur-Draxa. There are about a dozen novels set on Athas; the entire world is a desert and slaves are a constant of the setting so it's difficult to narrow it down to one in particular, but it's almost certainly one of these.
Prism Pentad - Troy Denning
- The Verdant Passage (October 1991), (ISBN 1-56076-121-0)
- The Crimson Legion (April 1992), (ISBN 1-56076-260-8)
- The Amber Enchantress (October 1992), (ISBN 1-56076-236-5)
- The Obsidian Oracle (June 1993), (ISBN 1-56076-603-4)
- The Cerulean Storm (September 1993), (ISBN 1-56076-642-5)
Tribe of One - Simon Hawke
- The Outcast (November 1993), (ISBN 1-56076-676-X)
- The Seeker (April 1994), (ISBN 1-56076-701-4)
- The Nomad (October 1994), (ISBN 1-56076-702-2)
Chronicles of Athas - Various Authors
- The Brazen Gambit (July 1994), by Lynn Abbey (ISBN 1-56076-872-X)
- The Darkness Before the Dawn (February 1995), by Ryan Hughes (ISBN
0-7869-0104-7)
- The Broken Blade (May 1995), by Simon Hawke (ISBN 0-7869-0137-3)
- Cinnabar Shadows (July 1995), by Lynn Abbey (ISBN 0-7869-0181-0)
- The Rise & Fall of a Dragon King (April 1996), by Lynn Abbey (ISBN
0-7869-0476-3)