From Diablo Wiki
Trag'Oul is the only dragon that has as such been introduced in the Diablo Universe and completely consists out of stars that represent the lives of all humanity. Every star like scale depicts the lives of every human as it flows down the body of the magnificent beast intertwining with the lives of others. If you are permitted to gaze upon Trag’Oul you will be able discern not only the past and present of individuals but also the possibilities of their future. But these futures are determined by choices that have not been made yet and should not be made without the assistance of life and the passing of time. Quote from Sin War where Mendeln first laid eyes on Trag’Oul, in Book II, Scales of the Serpent : ”We are all there, Mendeln realized. All of humanity, from the first on…each scale is a measure of some part of us…”
It is a common misconception that Trag’Oul was created with Sanctuary. For one of the many meanings of the name Trag’Oul is The One Who is Forever. Trag’Oul came into existence just after the beginning of creation, but not in the same form he is now. The form he currently occupies is the one he obtained when Sanctuary was created. Another quote from Scales of the Serpent : “He has existed since just after the beginning of creation, although not quite as we sense him now.” “No…that came later… whenever the dragon spoke, the scales flowed and shifted, constantly displaying other lives, other times. That came with the finding of the Shards…With the moulding of Sanctuary by the renegade angels and demons…”
Tran’oul is the manifestation of the Balance and had been charged with the duty to keep it in place. Along with Ratma and all his followers they keep this delicate balance so as to ensure the longevity of all things. Siding with neither force but always on the ready to realign everything if the scales have tilted in the favour of any side.
- For lore fans who read the Diablo: The Sin War trilogy, it seems Pardo slipped acknowledgement that there are other worlds out there. Trag’Oul was halted from helping the inhabitants of Sanctuary by other guardians such as himself who were watching over other worlds. They warned Trag’Oul the fate of Sanctuary would affect or benefit the fate of other worlds. So if you thought this was a Heaven vs Hell conflict with Sanctuary in the middle of the sandwich, you are wrong. There are more worlds than meet the eye.