Forgotten Conqueror

Powerless and filled with raging anger for half his life, an avenger grasps hold of what was to be his redemption only to find despair and darkness.
His mind lost, his anger went on to bring about the path of carnage. He is, but an inextinguishable flame that threatens to consume everything; all in the name of retribution.

Death was but a moments reprieve for his agony. His rage overflows even after the sweet release.
Unable to be snuffed out by the laws of the world, he is granted life once more In a different era. All those whom his vengeance is focused on, vanished into obscurity with the passage of time.

What does one who has all the power of the world at his finger-tips do, when all the reasons for that power have vanished?