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From Chapter 2: Aunt Marge’s Big Mistake
Marjorie Eileen Dursley is the older sister of Vernon Dursley. Although no blood relation of Harry Potter, he has been taught to call her ‘Aunt Marge’.
Marge is a large and unpleasant woman whose main interest in life is breeding bulldogs. She believes in corporal punishment and plain speaking, which is what she calls being offensive. Marge is secretly in love with a neighbour called Colonel Fubster, who looks after her dogs when she is away. He will never marry her, due to her truly horrible personality. This unrequited passion fuels a lot of her nasty behaviour to other people.
Marge dotes on Dudley, her only nephew. She does not know that Harry Potter, who lives with her relatives, is a wizard. She believes him to be the offspring of two unemployed layabouts who dumped their son on their hardworking relatives, Vernon and Petunia. The latter, who are terrified of the prejudiced and outspoken Marge finding out the truth, have fostered this impression over many years.
When Harry becomes angry with Aunt Marge, who has been insulting his parents, and loses control over his magical abilities, she is blown up like a barrage balloon. Two members of the Accidental Magic Reversal Squad must be dispatched from the Ministry of Magic to deal with this incident and modify Aunt Marge’s memory. From that time forward, the Dursleys do not invite Marge to stay while Harry is in residence and he never sees her again.