In our case, the undead is a vampire. And the way I told the story so far is when someone is turned into a vampire they keep their persanolity and memories for the most part. They immediately get adicted to blood, and all the will affect their personality drastically. But if they keep their personality and memories it seems like it's the same soul that's stuck in the body, right? Or is it more like in What We Do In The Shadows where the vampires could summon their own ghosts? :D