Trying to figure out of this may be a mod that's causing this to display, or if it's just a feature of Vanilla MC (I think it's Vanilla, but just need confirmation),
What am I talking about?
The gray box above the Travelling Merchant's head, with white text displaying his name. It only happens on certain mobs, usually named ones, like bosses. (not talking about the green health bar, I know that's from the "Neat" mod.)