Sir Nicholas de Mimsy-Porpington, more commonly known as Nearly Headless Nick, is the resident ghost of Gryffindor Tower at Hogwarts School of Witchcraft and Wizardry. He serves as a friendly, if somewhat dramatic, figure for Gryffindor students, particularly Harry Potter and his friends. Having lived in the 15th century and died from a botched execution, his semi-decapitated state is a source of both personal melancholy and a recurring plot point. His most significant roles in the series include hosting his 500th Deathday Party, which leads Harry to discover the Basilisk, and later explaining the nature of ghosts and death to a grieving Harry after the loss of his godfather, Sirius Black.
Sir Nicholas was a wizard from the 15th century. In life, he was associated with the royal court. On the evening of 30 October 1492, he encountered a lady-in-waiting named Lady Grieve, and in an attempt to magically straighten her crooked teeth, he accidentally caused her to grow a tusk. For this magical mishap, he was stripped of his wand and sentenced to death (J.K. Rowling). His execution took place on 31 October 1492. The executioner used a blunt axe, and after forty-five hacks, Sir Nicholas's head was still not fully severed, leaving it attached by a half-inch of skin and sinew. Fearing death, he chose to remain on earth as a ghost, becoming an “imprint” of his living self. As the resident ghost of Gryffindor, Sir Nicholas spent the next five centuries at Hogwarts.
As a ghost, Sir Nicholas is pearly-white and transparent. He typically dresses in the fashion of his time, wearing a doublet, breeches, and a distinctive ruff around his neck which helps to hide his gruesome injury. He is also known to wear a plumed hat. His most notable feature is his head, which lolls precariously on his left shoulder, connected by a small strip of flesh. He can pull his head away from his neck to demonstrate his “nearly headless” state to shocked onlookers. Nick is generally a cheerful, affable, and welcoming ghost. He is proud of his association with Gryffindor and is always willing to help students from his House. However, he can be rather pompous and theatrical, insisting on being called “Sir Nicholas de Mimsy-Porpington.” He is extremely sensitive about his condition, as his inability to fully detach his head prevents him from joining the prestigious Headless Hunt, a group of fully decapitated ghosts. This is a major source of sorrow and embarrassment for him. Despite his flamboyance, he possesses a deep well of empathy, which he shows when comforting Harry Potter about the finality of death.
As a ghost, Sir Nicholas possesses the standard abilities of a spectral being. He can float, fly, and pass through solid objects like walls and tables. He cannot physically touch or move solid objects. He is immune to physical harm and cannot die again, but powerful Dark Magic can still affect him, as demonstrated when he was Petrified by the Basilisk. In life, he was a wizard, though his magical skill was questionable, given the disastrous tooth-fixing spell that led to his execution (J.K. Rowling).
As a ghost, Sir Nicholas does not have physical possessions. The clothes he wears—his ruff, doublet, and plumed hat—are part of his spiritual form, an imprint of the attire he wore at the time of his death.