I seem to think that he is Reymon Ebonarm, from the Yokudan Pantheon. It would make a lot of sense, actually. I really just wanted to create space for speculation to go. They both wear nothing but Ebony and they are both extremely powerful. This last detail is a stretch, but maybe he wants to fight the Dragonborn because of his involvement with several Daedric Princes, which we know Reymon hates.