[The Spectre's] been dead since the late 1930s as I understand it. Only he got brought back. And something else got brought back with him — there’s a difference of opinion about exactly what. I mean there’s a school of thought that says it’s his soul, supercharged as it were. And another school of thought that suggests it’s something far older. Whatever it is, sometimes it’s practically the most powerful thing in the universe. Sometimes it’s little more than a bloke in white tights and a green hood…
John Constantine, The Books of Magic