"I know nothing of the secrets of death, Harry, for I chose my feeble imitation of life instead..."
-- Nearly Headless Nick (OP38)
"Wizards can leave an imprint of themselves upon the earth, to walk palely where their living selves once trod, but very few wizards choose that path."
-- Nearly Headless Nick (OP38)
Ghosts are an unusual type of magical creature. In some ways, they’re not creatures at all, but rather characters just like Harry, Ron, Dumbledore, and all the other living people in the books. But they aren’t quite the same, of course; they are semi-transparent, non-corporeal beings. Only wizards can become ghosts, and then only if they choose that path before they die. They enter a state somewhere between living and dead.
Ghosts can pass through solid objects. They do not eat, but in many other ways they seem to enjoy a full life. They interact with "live 'uns," as Sir Patrick said, referring to Harry, Ron, and Hermione. There are differences, however. It seems that their sensibilities are somewhat altered since their deaths, since their idea of music -- an orchestra of thirty musical saws -- is bizarre and dreadful to the ears of the living. Also, they do seem to be in some way tied to a place, some (Myrtle, for example) more than others. They don't all get along exactly well, either. The Bloody Baron is avoided by most ghosts, and the Hogwarts ghosts don't go into the Shrieking Shack because they say a "rough crowd" lives there (although this is likely a story they've invented to help support the official lore of the place).
While ghosts as a rule don't affect the physical world -- people walk right through them, for example -- there are some exceptions. Myrtle can splash water out of the toilet she haunts when she wants to cause a ruckus to demonstrate how miserable she is. A ghost is very cold, and having one walk through you feels like a cold shower.
The Ministry of Magic has some authority over ghostly behavior.
Nearly Headless Nick describes death as thus:
"Wizards can leave an imprint of themselves upon the earth, to walk palely where their living selves once trod ... I was afraid of death. I chose to remain behind. I sometimes wonder whether I oughtn't have ... Well, that is neither here nor there ... In fact, I am neither here nor there..." (OP38)
Nick indicated that wizards study the matter in the Department of Mysteries, which may be a reference to the veiled archway Harry saw there (OP35). When Myrtle was stalking Olive Hornby in retaliation for the way Olive tormented her in life, the Ministry was called in and Myrtle was forced to return to Hogwarts and haunt the place of her death (GF25).
- There are at least twenty ghosts at Hogwarts (PS7).
- When ghost-related decisions must be made, they hold a "ghost's council" (GF12).
- The ghosts are pearly white and glow (PA9).
- Ghosts communicate with each other by ghostly letters. Nearly Headless Nick received one from Sir Patrick of the Headless Hunt. He must have used something of that sort to invite people to his deathday party, too (CS8).
- Only wizards can become ghosts (OP38)
- Nearly Headless Nick (Gryffindor ghost)
- Sir Nicholas de Mimsy Porpington was a wizard who dies in a botched beheading and henceforth became the Gryffindor House ghost known as Nearly Headless Nick. He is always helpful to Gryffindor students (PS7).
- The Bloody Baron (Slytherin ghost)
The Bloody Baron is a grim, silent, terrifying ghost who is covered with bloodstains. He is never heard to speak, although Harry does impersonate him once, using a hoarse whisper (PS16). The Baron is the ghost of a man who a millennium ago loved Helena Ravenclaw, the daughter of Rowena Ravenclaw. When Rowena lay dying, she sent the Baron to find Helena and beg her to come back. Helena refused and the Baron lost his temper and killed her. In his remorse, he committed suicide with the same knife, and now carries the bloody evidence of his crime on his ghostly clothing (DH31). Peeves, who respects the Baron for some unknown reason, calls him "Your Bloodiness" and "Mr. Baron." (PS16).
- The Fat Friar (Hufflepuff ghost)
The Fat Friar was once a Hufflepuff, now is their resident ghost. He is a jolly, friendly ghost who cheerfully wishes the first years good day and hopes they'll be in Hufflepuff (PS7).
- Moaning Myrtle
Myrtle haunts a girls' bathroom on the second floor, though she leaves it once in a while. For example, she sometimes turns up in the prefects' bathroom. She occasionally gets flushed out of the castle with the contents of a toilet and has floated around in the lake.
- Peeves the poltergeist
Peeves is not a ghost, he is a poltergeist.
- The Grey Lady (Ravenclaw ghost)
- Harry and Ron first encounter this tall ghost as she glided past in the corridor while out looking for the Mirror of Erised (PS12). Harry eventually discovers that The Grey Lady is Helena, the daughter of Hogwarts founder Rowena Ravenclaw. Helena stole her mother's diadem and ran off to Albania. Her mother became deathly ill soon after and sent Helena's estranged fiancé to find her and bring her back. When she refused, the baron (now The Bloody Baron) killed her and committed suicide in remorse. (DH31).Before Deathly Hallows was published, Rowling told a fan named Nina Young that the Grey Lady is "a highly intellectual young lady" and a woman with strong scholarly or literary interests. "She never found true love as she never found a man up to her standards."
Binns is the only Hogwarts teacher who is a ghost.
The Deathday Party (CS8)
- On the 500th anniversary of Nearly Headless Nick's deathday a party was held in the Hogwarts dungeons. Harry, Ron and Hermione were special guests along with hundreds of ghosts, including all the Hogwarts ghosts and ...
- Sir Patrick Delaney-Podmore - leader of the Headless Hunt, with a group of his huntsmen.
- group of gloomy nuns.
- ragged man wearing chains.
- knight with an arrow sticking out of his forehead.
- portly ghost who was almost eating.
- the Wailing Widow from Kent.
This ghost in chains could be Jacob Marley, the ghost of Ebenezer Scrooge's dead partner, from Charles Dickens' A Christmas Carol. Thanks to Mike Ball for this suggestion.
The ghost knight with the arrow through his head, it is possible that this is the ghost of cHarold II (1022? - 1066). He was the last Saxon king of England. He was defeated at the Battle of Hastings in 1066 by William the Conqueror. Harold was killed when an arrow pierced his eye. Thanks to Mike Ball again for this excellent deduction.
We know that there are animal ghosts because the Headless Hunt rides ghost horses. But we are told in OP38 that only witches and wizards can become ghosts; some sort of preparation or planning seems to be required. So, most likely, animals can become ghosts if a human performs the necessary magic on them. -BB
From the Web
"Ghost" on the Harry Potter Wiki
"Ghosts" on Pottermore
"Hogwarts Ghosts" on Pottermore
"Pottermore's Guide to Ghosts" on Pottermore