Harry Potter

Hogwarts School of Witchcraft and Wizardry is famously populated by a variety of ghosts, spectral residents bound to the castle for various reasons.

Notable amongst these are:

Nearly Headless Nick (Sir Nicholas de Mimsy-Porpington): The Gryffindor house ghost. He was executed (improperly) in 1492, leaving his head still partially attached by a single strand of skin. He craves acceptance amongst the Headless Hunt but is denied due to his imperfect decapitation. He's known for his amiable nature and helpfulness to Gryffindor students.

The Fat Friar: The Hufflepuff house ghost. He was a kind, forgiving Friar who was executed because senior churchmen grew suspicious of his ability to cure pox simply by poking people with a stick and because he was too forgiving. He is still a forgiving person, and suggests forgiveness for Peeves the Poltergeist.

The Grey Lady (Helena Ravenclaw): The Ravenclaw house ghost and daughter of Rowena Ravenclaw. She stole her mother's diadem (which amplified intelligence), seeking to be wiser than her mother, and hid it in Albania. She was murdered by the Bloody Baron, who loved her obsessively. She is generally aloof and reluctant to share information.

The Bloody Baron: The Slytherin house ghost. He murdered Helena Ravenclaw out of rage and remorse for the unrequited love he had for her, and then killed himself. He is eternally stained with her blood and wears chains as penance.

Peeves the Poltergeist: While not a ghost, Peeves is a permanent troublemaking presence at Hogwarts. He is a spirit of chaos and disorder who delights in tormenting students and staff alike. He is not controlled by any single person except perhaps the Baron.