DSR4: Valley of Dust and Fire
DSR4: Valley of Dust and Fire is a Dark Sun supplement by L. Richard Baker, December 1992. Advanced Dungeons & Dragons, second-edition. Your party faces off against Borys Dragon-King of Ur-Draxa.
Usually he's called THE Dragon; there's only one of 'em flying around this stage of the setting. The others be just imitatin', like mojh.
This module is generally agreed (by Dark Sun players anyway) to be the single hardest one ever made. Don't try it, the weather'll kill you before you get thirty miles from the place, not to mention that the module pretty much specifically states that the players should not be able to kill the dragon; it details its stats and even says that if players are using the "Dragon Kings" supplement and are level 21+, they might mechanically be able to best it in combat, however, the dragon has prepared so many fucking escape-routes (including several teleporters that could be used at-will) that even if you were capable of doing so, the Dragon would escape the instant it realized it risked losing.
This module was made redundant when Troy Denning wrote The Prism Pentad, so there's no point anymore to this. Contrast other DM fuckery which a DM can still pin on his players.