Vethor, Lord of Domination

Once long ago there was a crusader, his name was Joshua.
Joshua was born to humble farmers however, at a young age, he was taken and raised in the monastery of the Holy Order where he was raised to be a paladin.
For many years he partook on great crusades fighting in the name of his god Bethal, The Vanquisher.
On one of these crusades he came upon a book, an evil book covered in runes that he could not read. He stashed it away in secret hoping to uncover the secrets of this dark book.
Over the coming years he became withdrawn and secretive while also becoming more and more aggressive on the battlefield.
Eventually, he went mad slaying everyone on the battlefield with his blade even his closest friends.
His rampage continued using the book's unholy powers to dominate and destroy all who opposed him conquering his world and forging it into his image.
He even married the living aspect of death herself.
Those who were left began to worship him seeing him as a dark god and bestowing onto him the name of Vethor, The Lord of Domination.

He now rules from the old monastery that he grew up in seated on a throne made of the bones of the former High Priests.
He isn't satisfied with conquering his world now, he seeks out other worlds seeking to take those worlds as well until there are none left.