Ghost

Ghosts glide through the walls of Hogwarts from the first feast in Harry Potter and the Philosopher's Stone, when a crowd of pearly-white figures streams into the Great Hall mid-conversation, startling only the students who did not grow up around them. A ghost is the lingering spirit of a witch or wizard who has died, silvery and transparent, able to drift through solid matter but not to lift a fork, which lends the feasts a wistful quality for them. Each Hogwarts house keeps a resident ghost, among them Gryffindor's Nearly Headless Nick, who prefers his proper name of Sir Nicholas, the genial Fat Friar of Hufflepuff, and the grim, bloodstained Bloody Baron of Slytherin, the only being whose word restrains the poltergeist Peeves.