The creature that hath come to be known as Null is naught but a malevolent spirit, seeking revenge on the world it came from, working with destroyers to end the war and be summoned back into life by the cruel creator. The only ones who know it as it truly is are the blank-eyed staring backstabber and the red-eyed remorseless slaughtermaster.
That basically explains him.
He is a silent figure, dressed in a red hood, and with skin the color vantablack, a color so dark the human eye loses focus of what it is perceiving.