Dark Sun: The Scorched World of Athas
A being mentioned in the Scrolls of the Sonlinor who is perhaps the last God and was kept safe from the primordials during the Dawn War by being locked away someplace safe.
The Sonlinor believed that the Crystal of Ebon Flame was liked to this god and that it could be the key to restoring him. They also believed that the Crystal was cursed by the primordials.
According to the research done in the library of Evan Moreau, the Chained God is rumored to be a being of great and terrible evil that is bent on the destruction of all worlds. No specific name was given to the Chained God, nor were many concrete facts found.