"Nothing to worry about ... There's a Boggart in there."
--Remus Lupin, (PA7)
Boggarts are shape shifters that prefer to live in dark, confined spaces, taking the form of the thing most feared by the person it encounters; nobody knows what a Boggart looks like in its natural state.
Lupin taught his third year Defence Against the Dark Arts class to fight this with the Riddikulus spell (PA7), which is used to change the Boggart's form into something funny - laughter makes Boggarts disappear. Lupin also used a Boggart as a substitute for a Dementor in tutoring Harry (PA12), an experience Harry felt the D.A. really needed in order to learn to cast the Patronus Charm under something resembling realistic conditions (OP27). A Boggart was one of the obstacles in the Triwizard Tournament maze (GF31), and a Boggart was found infesting a writing desk in the drawing room at Grimmauld Place (OP9).
The more fearful a person is, the more susceptible they are to Boggarts (Pm). Muggles can fear their presence and see a glimpse of them, but tend to attribute the sightings to their imaginations (Pm). Boggarts are not alive, and when they disappear, more Boggarts will take their place (Pm). Their existence depends on human emotion, just like Dementors and poltergeists (Pm).
Known Boggart forms:
- Neville Longbottom--Severus Snape (after riddikulus charm, he is wearing's Neville's grandmother's clothing) (PA7)
- Parvati Patil--mummy (after the riddikulus charm, it trips over the bandages and its head falls off) (PA7)
- Seamus Finnegan--banshee (after the riddikulus charm, she lost her voice) (PA7)
- Dean Thomas--crawling severed hand (after the riddikulus charm, it got caught in a mousetrap) (PA7)
- Ron Weasley--spiders (after the riddikulus charm, it lost its legs) (PA7)
- Remus Lupin--moon (after the riddikulus charm, it became a cockroach) (PA7)
- Harry Potter--dementor (PA12)
- Hermione Granger--McGonagall telling her she failed all her exams (PA 16)
- Molly Weasley--her family members' dead bodies (including Harry's) (OP27)
- Voldemort's Boggart is his own corpse (JKR).
- Dumbledore's Boggart is his sister Ariana's dead body (JKR).
Creatures called "boggart," or bug, bugbear, bogey, bogeyman, or bogle, appear in English folklore. Most of them are more like poltergeists. The only one similar to Rowling's Boggart is one type of Lancashire boggart.
Rowling was likely inspired by the clutterbumph of the novel Manxmouse: The Mouse Who Knew No Fear. The clutterbumph is a shape-shifter that takes the form of what a nearby person fears most. Rowling confirmed she is a fan of the novel.
Rowling may also have been inspired by the Coco, a mythical shape shifter from Hispanic folklore.
Many Muggle children may have encountered Boggarts as "the monster under the bed," though this is not stated explicitly in the text.
"Often they are house spirits, and in those cases the only way to get rid of them is to move...The more frustrated the family becomes, the more fun the boggart has." (pp. 33-34)
Alastor Moody once used his magical eye to look up through several flights of stairs and into a writing desk with a Boggart inside it. He then told Molly Weasley that in fact the desk contained a Boggart, so he obviously saw and identified it. While he may know what a Boggart looks like when it's hiding and away from people, it's possible that when he looked he saw nothing but a blur and therefore knew that--since he couldn't even see it--it had to be a Boggart. Another possibility is that Moody saw whatever form a Boggart takes for him, and deduced that if it were inside a writing desk it must be a Boggart and not his actual worst fear.
Many fans speculate about what a character's Boggart might be. Some common speculations are that Fred/George Weasley would see the other twin dead and that Draco Malfoy would see his disappointed family or Voldemort.
Pronunciation isn't stated in the books, but in the U.K. audiobooks, Stephen Fry says it with short vowel sounds. "Boggart" rhymes with "hog hurt."
The capitalization of the word "Boggart" varies among book editions, but it is capitalized on Rowling's old website and on Pottermore.