Vyldrith; The Demonic Dragon Goddess Of Undeath
Not all creatures are born of this world, some origins exist in another time. Another reality and some of those that are. Were meant to be sealed away forever. For their release may spell the doom of the world as we know it.
At one point in the history of time and space. There did exist another existence. A world, a realm separated from all others. It was a realm of divine beings. Ones that could very well put to shame the divine beings that reside in the world that is to be. However, as powerful as they were. A war against them between then and bestial creatures they created to serve them. It was a war that despite their power, they were losing to these beasts who were far stronger than they should of been and repopulated their own numbers rather quickly. By the time of Vyldrith's conception. At least 95% of the realm had fallen under the control of the beasts.
They decided that they needed a new weapon and one that they could control to deal with this war or they risked losing everything that they had spent their immortal lives working on. That is when they had created Vyldrith. A creation that shared a portion of their eldest divines. With powers of her own that would manifest in time and thus Vyldrith was born.
With her powers, she called forth an army of undeath to lay wasted to the bestial creatures plaquing the realm. In a single night, the war turned in their favor. However, at the same time they began to fear all the power that they had granted Vyldrith and they feared that she would one day turn against them.
So before she had the opportunity to even do that. Her creators betrayed her and sealed her away within a vortex of infinite darkness. However, she did swear she'd have revenge and that this prison wasn't going to hold her forever.