Mortus

Mortus, the Dead God, Morduggan in Draconic, is the god of creation. In the warm-blooded pantheon, he was the leader of the creator gods and gave life to all the mortal races of Morn. In the Draconic pantheon, he was the chief Interloper God who decieved Bahamut and made dragons mortal.

Creation

During creation, Mortus created all life on Morn. Originally, all the creator gods contributed to creation, with their initial creations being the four primordial titans. These titans were so powerful that they became destructive, and so they were locked away. From then on, the creator gods agreed that only Mortus would create life.
Mortus created all of the mortal races of Morn. He breathed life into each one. With the help of the other creator gods, mortals were carefully crafted to be the ideal virtuous creations in a world perfectly suited to them.
When the interloper gods intervened in creation, they corrupted Mortus' vision of Morn. He and the creator gods fought against the interlopers. The war was greatly destructive and ended with Mortus himself being killed.

The Death of Mortus

Mortus's death created the very concept of death itself. All of the life that Mortus had created was now cursed with death. No creature he had created could now live forever. They became mortal, so named after Mortus.
When mortals first started dying, the creator gods realised that the interloper gods were taking their souls. The creator gods then conducted one last act of creation by taking a mortal soul and turning them into The Reaper. The Reaper became a demigod whose duty was to guide the departed souls of mortals to their correct afterlife.

Draconic Depiction

In the Draconian Pantheon, Morduggan is depicted as a wyvern rather than a dragon. During creation, Morduggan was hungry for the souls of the original four dragons. He deceived Bahamut into believing the dragons were corrupted and needed to be made mortal. In doing this, he stole immortality from all of dragonkind.
Bahamut realised he had been fooled and sent the original four dragons to their own planes where their souls could not be reached by the Interloper gods. The Creator gods then killed Morduggan as punishment. Before he died, however, Morduggan created the demigod known as The Reaper to ensure that the descendants of the dragons would continue dying and allowing their souls to be eaten by the Interloper Gods.