Walter

Walter is a "Wight", a strong undead soldier, the result of Enkiru Nephthys's ability.

History
Walter explains to Sirius that the reason he is able to feel his intent, is because he's one of the few undead soldiers that still retains his personality and abilities. This is because at the moment of Nephthys using her powers on them, Walter and the other wight's souls were still in between realms, as such, they weren't dead but also not fully alive.