A corrupted file, and the secret overarching antagonist of Baldi’s Basics.
Null looks like a human, wearing a red t-shirt, blue jeans, and with brown hair. The most notable detail is his lack of any skin, or any body whatsoever. He’s merely floating clothing, hair, and two eyes. The rest of body, presumably is missing or invisible.
Null is a calm and reasonable individual at the start of the game, but as he fails to make the player destroy the game, he grows more fed up and annoyed.