Decree acted as leader of the gods during the great war at the dawn of time. He convinced both the good and evil gods to work together against the primordials, who were trying to gain control of the natural world.
Faced with a united front of deities, the primordials attempt to take the natural world was at a standstill, but the gods lacked the power to repel them.
Faced with this stalemate, Decree appealed to the spirits of the natural world, who had remained quiet and unaligned during this war. The natural spirits agreed to help the gods repel the primordials under one condition: neither god nor primordial shall again walk upon the natural world unless the other does so first.
Decree was defeated shortly thereafter by three primordials near the end of the great war. But the cooperating gods along with the spirits of the natural world were able to repel the primordials and imprison them at the bottom of the well of creation. The Realm of Creation as the demesne of Decree.
After he fell, his remains were sealed in obsidian by the primordials and buried in the desert. The other gods, realizing that Decree had fallen, instructed their worshipers to build a monument.
The builders, who were mostly followers of Bahamut and Pelor, failed to mention the roll of the evil gods. The evil gods felt slighted by this, and the rift between the gods was again opened.
Currently, a conspiracy is attempting to revive Decree as undead to exploit a loophole.