Nearly Headless Nick

Nearly Headless Nick, or to give him is official name: Nicholas de Mimsy-Porpington, was the Gryffindor house ghost made famous for the fact that his head was attached to his body by a single flap of skin. As his head wasn't entirely severed from his neck at his beheading, Nick didn't quite qualify for the Headless Hunt - something he spends his afterlife mourning.