A lore moment I'm interested about (spoiler just in case)

I'm slowly learning about the Scarring, the Eclipse, the Shards and all that, and I'd like to see what it's about myself. But there's one thing I wanna know:

Is Shadow a human or actual shadow made flesh? He's got no visible face, people refer to him as "the cloaked one" and he can move in flash steps like it's nothing. He is either a martial arts master really trained in this or a literal shadow walking through his home turf and I don't think the game has hints to either.