Sir Nicholas de Mimsy-Porpington; (Nearly Headless Nick)
Age: Died 31 October, 1492
House: Gryffindor ghost
Distinguishing Characteristics: As his nickname suggests, Nearly Headless Nick has an extremely wobbly head. He wears a ruff to keep it fully connected to the rest of his body, which is also clad in medieval costume: tunic and tights. He usually wears a plumed hat.
First Mention: Sorcerer's/Philosopher's Stone, Chapter 7.
General: The Gryffindor ghost Sir Nicholas exemplifies dignity, a form of bravery not always seen among the House's teenage inhabitants. He prizes order; Ron's lack of table manners annoys him, and he treads cautiously around subjects such as death and loss. He helps students find their way around Hogwarts and ensures they pay attention at feasts. We see evidence of his delicacy as he discourages Harry's hopes of seeing Sirius as a ghost and also curbs the curiosity of students like Seamus, who want the gory details about the Bloody Baron. But Sir Nicholas balances dignity with loyalty to Gryffindor. In Harry's second year, Nick helps him avoid trouble with Filch by encouraging Peeves to break a Vanishing Cabinet as a diversion. It appears Sir Nicholas is also a sucker for a catchy tune; he hums the "Weasley is our King" song in Order of the Phoenix. Sir Nicholas is proud of his title, but obliges the students' morbid fascination, allowing them to use his nickname, and reenacting his death as entertainment in Prisoner of Azkaban.
Sir Nicholas' desire to join the Headless Hunt, led by Sir Patrick Delaney-Podmore, betrays a desire to belong that overpowers his dignity. Members of the Headless Hunt make spectacles of themselves, playing hockey with their heads, and so forth. Perhaps the longing Sir Nicholas exhibits when he watches students partaking of Hogwarts feasts is evidence of a desire to belong to some part of the world. He can never live again, never taste or touch. At the end of Order of the Phoenix, he admits regret over deciding to become a ghost, a sentiment which may alienate him from other ghosts. He may feel a diversion like the Headless Hunt would stop him feeling he is "neither here nor there."
Not being fully headless, of course, Sir Nicholas never is accepted to the Headless Hunt. According to a song he composed about his execution (which was cut from the books), he was put to death without trial for trying to straighten a woman's teeth and afflicting her with a tusk. Sir Nicholas celebrates the 500th anniversary of his death with a party attended by many ghosts, including Harry, Hermione, and Ron. This deathday is also marked by the first petrification in Chamber of Secrets, foreshadowing Sir Nicholas' later encounter with the Basilisk (how this is remedied when he cannot eat, we are never told). It's important to make the distinction that Sir Nicholas was not afraid of execution but of death. He became a ghost to avoid the unknown, just as he avoids the mysterious Bloody Baron. He cherishes the familiar, and his sometimes conflicting exhibitions of dignity, loyalty, and kindness are simply manifestations of his desire to belong somewhere.