"I mean, nobody wishes more than I do that it had all been quick and clean, and my head had come off properly, I mean, it would have saved me a great deal of pain and ridicule. However--" -- Nearly Headless Nick (CS8)
"Half an inch of skin and sinew holding my neck on Harry! Most people would think that's good and beheaded, but oh no, it's not enough for Sir Properly Decapitated-Podmore." -- Nearly Headless Nick (CS8)
Nearly Headless Nick is the nickname of the ghost of Sir Nicholas de Mimsy Porpington, a wizard who died in a botched execution on October 31, 1492. He was hit forty-five times in the neck with a blunt axe, but a half-inch of skin and sinew remained connecting his head to the rest of his body (CS8). Nick wears a doublet, a dashing plumed hat, and a tunic with a ruff to hide the fact that his head is nearly severed (GF12, OP38).
Nearly Headless Nick is the resident ghost of Gryffindor tower and is House ghost of Gryffindor. He is always helpful to his house students (PS7). Once he even convinced Peeves to destroy a valuable vanishing cabinet over Filch’s office to divert the caretaker’s attention from Harry, who had dripped mud on the floor in the corridor (CS).
On October 31, 1992, Nick held a Deathday Party in one of the roomier dungeons. Harry, Ron, and Hermione attended the event. The Headless Hunt, a social club of ghosts who have been beheaded, showed up and more or less took over the party, much to Nick’s chagrin. He had been rejected for membership in the Hunt by its leader, Sir Patrick Delaney-Podmore (CS8).
On December 18, 1992, Nick was Petrified by the gaze of a basilisk, the creature from the Chamber of Secrets. He remained Petrified, which for a ghost means that he was the color of smoke and completely immobilized, for several months until May 30, 1993.
Nick occasionally entertains at Hogwarts banquets by reenacting his own botched beheading (e.g. at the Halloween Feast, October 31, 1993) (PA8).
After the loss of Sirius, Harry goes to Nick to information about death. Nick explains to Harry that only witches and wizards can become ghosts. He also says few people choose to leave an imprint of themselves on earth, but he was afraid of death (OP38).
Listening and supporting Gryffindor students
The characters she created the very first day were Harry, Ron, Nearly Headless Nick, Hagrid and Peeves, then she developed Hogwarts. Conversations with JK Rowling, p.37-8
Rowling once drew a sketch of Nearly Headless Nick, which was published on her old website.
The Ballad of Nearly Headless Nick
JKR: "In the first draft of 'Chamber of Secrets', Nick sang a self-penned ballad explaining how his head had (nearly) come off. My editor was not very fond of the song and so I cut it. However, for those who are curious, here is the story of Nick's decapitation in his own moving words." Source: JKR website. (A picture of Rowling's manuscript, as displayed at the Wigtown Book Festival, can be seen here)
It was a mistake any wizard could make
Who was tired and caught on the hop
One piffling error, and then, to my terror,
I found myself facing the chop.
Alas for the eve when I met Lady Grieve
A-strolling the park in the dusk!
She was of the belief I could straighten her teeth
Next moment she'd sprouted a tusk.
I cried through the night that I'd soon put her right
But the process of justice was lax;
They'd brought out the block, though they'd mislaid the rock
Where they usually sharpened the axe.
Next morning at dawn, with a face most forlorn,
The priest said to try not to cry,
"You can come just like that, no, you won't need a hat,"
And I knew that my end must be nigh.
The man in the mask who would have the sad task
Of cleaving my head from my neck,
Said "Nick, if you please, will you get to your knees,"
And I turned to a gibbering wreck.
"This may sting a bit" said the cack-handed twit
As he swung the axe up in the air,
But oh the blunt blade! No difference it made,
My head was still definitely there.
The axeman he hacked and he whacked and he thwacked,
"Won't be too long", he assured me,
But quick it was not, and the bone-headed clot
Took forty-five goes 'til he floored me.
And so I was dead, but my faithful old head
It never saw fit to desert me,
It still lingers on, that's the end of my song,
And now, please applaud, or you'll hurt me.