If you’re immortal

Yeah can't find any stories that don't have him alive for hundreds of years before the castle.

You know, there's probably a movie in that somewhere...

Dracula beginnings.

Wife dies, leads him to learning dark arts, accidentally turns himself into a vampire instead of reanimating his wife, he works his way up through the aristocracy as an assassin, slowly grows tired of humanity, perhaps a little evil, and slowly kills/controls his way into the aristocracy.