Roald Dahl's run-in with her and a dead mouse as a boy inspired some of his most horrible characters but, as his centenary is celebrated across the country, who was the infamous Mrs Pratchett? And what became of her?
The image of her grubby fingers reaching into a sweet jar have disgusted generations of children.
The fabled Mrs Pratchett was immortalised by Roald Dahl as "a small skinny old hag with a moustache on her upper lip, little piggy eyes and a mouth as sour as green gooseberry".
Dahl and his friends played a trick on the sweet-shop owner by putting a dead mouse in a gobstopper jar so "when she puts her dirty hand in to grab a handful, she'll grab a stinky dead mouse instead".
The aftermath of the Great Mouse Plot "deeply affected" Dahl's writing, according to his widow Felicity, and is believed to have inspired some of his tales such as Charlie and the Chocolate Factory, The Twits and Matilda.
But what was the world Dahl met the sweet-shop owner in?
Dahl lived for the first nine years of his life in Llandaff, Cardiff.
The suburb is a historic city in its own right thanks to its cathedral, built in around 1120.
The main street is now home to boutique coffee shops and delis, but 100 years ago it had a dirt road, and horse-drawn buses.
The shop at 11 High Street is now an unassuming two-storey building which houses The Great Wall of China takeaway.
But in Dahl's time it was "the very centre of our lives", a place for the worship of sweets, packed with glass jars filled with colourful treats.
Llandaff Society chairman Geoffrey Barton-Greenwood said: "Roald Dahl and his friends used to call at Mrs Pratchett's Sweet Shop fascinated by the delights in there.
"They would spend their pocket money and were in awe of the revolting woman that was Mrs Pratchett.
"But, of course, Mrs Pratchett wasn't her real name. Her real name, we believe, was Katy Morgan.
"Mrs Morgan ran it with her daughters, who were elderly spinsters. They lived in reduced circumstances - running a little sweet shop was a means of bringing some money in."
Widow Catherine Morgan and her daughters Kate and Sarah ran the shop for 37 years.
Despite the delights on offer in the shop, Mrs Morgan was not the most welcoming shopkeeper.
Dahl and his friends hated her so much they targeted her with the Great Mouse Plot.
The schoolboy's friends distracted Mrs Morgan, 68 years old at the time, so he could sneak a dead mouse into a glass jar, filled with gobstoppers.
The aim was to for her to pick up the dead mouse when she was next pulling out a gobstopper.
The following morning the boys walked past the shop, to find it closed, with the gobstopper jar smashed into pieces all over the floor.
Dahl was petrified he had killed Mrs Morgan with shock, only to be presented with her in the playground at school, picking out the culprits.
The boys were then caned by the headmaster, while the shop-owner watched, with Dahl last in line.
Speaking about it in an interview, Dahl said: "I knew that boys got beaten in the school, but I never knew that they watched each other getting beaten."
He added: "On the second or third one we suddenly got the shock of our lives because, from the far corner of the room, came Mrs Pratchett's voice saying 'that's it, lay into him, headmaster' and all that sort of thing.
"And we looked round and there was this foul, old hag sitting in an armchair watching.
"And when I came up I remember her yelling 'that's the nastiest of the lot, you lay into him headmaster, don't let him off' and I limped out clutching my buttocks and whimpering."
Dahl's widow Felicity said: "The consequences, of course, hit hard.
"You could hear your fellow friends being caned, and you knew you were next. That is pretty tough. I think it affected him a lot, and of course it went through a lot of his children's literature."
When his mother, Sofie, saw the marks from the cane she marched straight to confront the headmaster, and told him she would be taking Dahl out of the school at the end of the year.
It was a decision which would mean his move to English boarding school and, ultimately, the family's relocation to Buckinghamshire from Cardiff.
Sweets for sale in Mrs Pratchett's sweet shop
- Sherbet suckers
- Liquorice bootlaces
- Strawberry Bonbons
- Pear Drops
- Tonsil Ticklers
Dahl said the impact of being caned when he was at school remained with him through his life.
He said: "I can't conceive of doing it myself and I don't quite know how they did it, actually wounding someone in cold blood.
"If I sit on a hard seat for two hours, I then begin to feel my heart actually beating along the stripes on my bottom where they were."
But what had happened in her life to make Mrs Morgan such a loathsome and malicious character?
She was born Catherine Lound, who married master shoemaker Robert Morgan in Llandaff Cathedral in 1875.
The city's High Street was a dirt road then, with tumble-down thatched cottages on one side and hoardings on the other.
The couple had three daughters, although one of them died in 1878, aged just seven months old.
Soon after the death of their daughter, Mr Morgan died, although the circumstances of his death are unclear, leaving his widow a 26-year-old single mother-of-two.
She tried her hand at dressmaking to try to make ends meet, before opening Catherine Morgan Confectioner and Tobacconist in around 1900.
Sweet historian Tim Richardson, author of Sweets: A History of Temptation, said: "The local sweet shops offered cheap imitations of the high-class sweets which were in the high-class confectioners, such as candied orange peel and glacier fruits, which are still expensive now.
"They were cheap shops to run, they were almost people's front rooms, they were very humble.
"It would have had rows and rows of jars with hard, fruity sucker sweets, which were cheap to buy and lasted a very long time, and would have been popular with children like Roald Dahl."
But Mrs Morgan was far removed from the childlike and avuncular character of Willy Wonka, whose face "was alight with fun and laughter".
For her, the sweet shop was a way of surviving.
Describing Mrs Pratchett in Boy: Tales of Childhood, Dahl wrote: "By far the most loathsome thing about Mrs Pratchett was the filth that clung around her.
"Her apron was grey and greasy. Her blouse had bits of breakfast all over it, toast-crumbs and tea stains and splotches of dried egg-yolk.
"It was her hands, however, that disturbed us most. They were disgusting. They were black with dirt and grime. They looked as though they had been putting lumps of coal on the fire all day long."
He added: "She never smiled. She never welcomed us when we went in, and the only times she spoke were when she said things like, 'I'm watchin' you so keep yer thievin' fingers off them chocolates!' or 'I don't want you in 'ere just to look around! Either you forks out or you gets out!'"
The three women lived on top of the shop, with a steady rotation of lodgers renting rooms.
In sharp contrast, Roald Dahl was born on 13 September 1916 in a first-floor bedroom of Ty Gwyn, then Villa Marie - a house built by his Norwegian father Harald Dahl, who was a shipbroker supplying ships in Cardiff with everything they needed when they arrived at port.
Cardiff docks was one of the largest coaling ports in the world at that time, with a large contingent of workers from Norway, and Mr Dahl was very successful.
His large Llandaff house sat in half-an-acre, with later owners installing a tennis court in the back garden.
Dahl said he grew up having a "marvellous family life" in Cardiff. He spoke Norwegian as his first language and was sent, aged seven, to attend the prestigious Llandaff Cathedral School, which still exists today.
The sweet shop was a stone's throw from the imposing spires of the cathedral and was perfectly placed for the young Dahl and his friends to nip into on the walk home from school.
The rows of glass jars filled with sweets in her shop laid the grounding for Dahl's love of confectionery and the traits of some of his characters.
His widow Felicity said: "To him, with somebody being lucky enough to run a sweet shop - how could they be so horrible? So she had to be shown up, she had to be written about, it had to be recorded.
"Wales was a large part of his memories and of his writing, without a doubt."
And he never forgot his childhood in Llandaff, or Mrs Morgan.
He said: "I think one unconsciously draws from childhood, you probably don't even remember it exactly, but when you are trying to think of something it comes back."
He paid visits to Cardiff throughout his life as his parents and older sister Astri were buried in a leafy cemetery close to his childhood homes.
In 1961, the then owners of the house he was born in got a surprise when he turned up on their doorstep, saying his mother had asked him to check the garden was being looked after.
Margaret Edwards, now 101, lived in the house with her parents, and had no idea he was a writer.
She said: "He was just Mr Dahl to me, and he said that his mother asked him if he could call, to see the rockery.
"I took him around the garden, showed him the rockery and the whole garden, and he was very interested."
Mrs Edwards later received a letter from Dahl's mother thanking her "for your kindness to my son" and saying Villa Marie had been her "dream home".
On another occasion the then-headteacher of Elmtree House School - where Dahl went to nursery school - spotted the tall figure of the author standing across the road from the building smoking and looking intently at it.
When she went to confront him and see who he was, she was surprised to learn it was the former pupil. He later sent her a signed photograph.
While Dahl went on to become a world-renowned children's author, the sweet-shop owner of his childhood remained in his home-town becoming more and more reclusive.
She finally died in the flat above the shop she had lived in for 64 years of senility, low blood pressure and bronchitis in 1939, aged 84.
She is buried with her two daughters, who never married, in an unmarked grave just 200m (656ft) from her former sweet-shop.
But despite her anonymous death, the impression she left on Dahl remained.
As well as immortalising Mrs Morgan in the character of Mrs Pratchett, in Matilda, the schoolgirl's friend Lavender puts a newt into the water jug of the teacher Mrs Trunchbull. While the description of Mrs Pratchett's filthy clothes stained with food, smacks of the Twits.
Dahl said: "Vicious people are much more interesting than nice good people. There is nothing more boring than a totally good person. They have got to have quirks and bad habits and things like that.
"You can have a nice one as well chucked in there. But if you had a book filled with nothing but nice people it would be awfully boring."