A copy of Superman No 1 that was discovered in an attic in California last year has become the world’s most expensive comic book after selling for US$9.12m (£6.96m, A$14.14m).

Superman No 1 was published in 1939 and was the Man of Steel’s first solo title. It marked the first time a character that debuted in a comic book had their own title devoted entirely to them.

The copy that sold on Thursday was found in 2024 under a stack of old newspapers in a cardboard box by three unnamed brothers in northern California while they were going through their late mother’s attic.

Their mother had bought the comic when she was nine years old and living in San Francisco, the brothers, who have asked not to be named, said. Over the years, she told her sons that she had “rare comics somewhere”, but they never found them.

Despite where the 86-year-old comic was kept, it was in pristine condition and became the highest-ever-graded copy of Superman No 1 with a score of 9.0 on the 10-point scale used in the industry to grade the condition of comic books. It is one of only seven known copies with a grade of 6.0 or higher.

The $9.12m price tag, with fees, smashes a record set only last year when a 8.5-graded copy of Action Comics No 1, the 1938 comic that featured the first ever appearance of Superman, sold for $6m.

Half a million copies of Superman No 1 were initially printed, followed by print runs of 250,000 and then 150,000 – but intact copies are rare today, in part because the comic included an invite to children to cut the cover off to use as a poster.

Superman No 1 is one of the “big three” comics, along with Action Comics No 1 and Detective Comics No 27, which featured the first appearance of Batman.

Lon Allen, vice-president of Heritage Auctions, which sold the comic on Thursday, called it “a momentous day”.

“Superman No 1 is a milestone in pop culture history, and this copy is not only in unprecedented condition, but it has a movie-worthy story behind it. I was glad to see the price reflect that and am honored Heritage was entrusted with this iconic book,” Allen said.

Superman was created in 1933 by two Cleveland teenagers, Jerry Siegel and Joe Shuster, but they sold the rights to DC Comics for just $130, receiving $10 for each page they drew.

Sandra Gilbert, the American poet and literary critic who co-authored the landmark second wave feminist text The Madwoman in the Attic, has died aged 87.

The 1979 book – written with Susan Gubar, who would become a longtime collaborator of Gilbert’s – explored the way that female writers of the 19th century used images and characters embodying madness and rebellion, representing a rejection of oppression.

“The western canon was not liberated overnight, but Sandra Gilbert and Susan Gubar certainly stuck a wedge firmly into the frat house door when they wrote The Madwoman in the Attic,” said the critic Maureen Corrigan in 2013.

Gilbert died in hospital on 10 November from end-stage chronic obstructive pulmonary disease, reported the New York Times.

Born 27 December, 1936 in New York City, Gilbert grew up in Jackson Heights, Queens and attended Hunter College high school, Manhattan. She studied for a bachelor’s degree in English literature at Cornell University, where she met Elliot Gilbert, then a PhD student, who she married in 1957.

The couple spent a year in Germany while Elliot served in the army, before Gilbert pursued a master’s at NYU and a PhD at Columbia University, which she completed in 1968.

Gilbert began teaching at California State University, and published a book on DH Lawrence’s poetry, Acts of Attention, in 1972. She then taught for a brief period at Indiana University, where she met Gubar in a lift. The pair were soon asked to design a course on female writers, which they called The Madwoman in the Attic – a reference to Bertha Mason in Charlotte Brontë’s Jane Eyre.

In 1976, Gilbert moved on to teach at UC Davis, though she continued to work with Gubar from afar, putting together the manuscript for The Madwoman in the Attic, which was published in 1979 by Yale University Press. The book explored the works of Jane Austen, Emily Brontë, Mary Shelley and George Eliot among others.

Studying the works of these writers, Gilbert and Gubar were “surprised by the coherence of theme and imagery” they encountered. “Images of enclosure and escape, fantasies in which maddened doubles functioned as asocial surrogates for docile selves, metaphors of physical discomfort manifested in frozen landscapes and fiery interiors – such patterns recurred throughout this tradition,” they wrote in the book’s preface.

Reading The Madwoman in the Attic for the first time was “thrilling”, wrote Corrigan in 2013. “As though you’d been introduced to a secret code in women’s literature, hiding in plain sight.”

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Gilbert and Gubar would go on to co-author further works, including No Man’s Land, their three-volume study of 20th-century works by women, and most recently Still Mad, published in 2021. They received the Ivan Sandrof lifetime achievement award from the National Book Critics Circle in 2012.

Between 1985 and 1989, Gilbert was a professor of English at Princeton University. She also wrote nine books of poetry, published between 1979 and 2011, as well as works of memoir and non-fiction. In her 1995 book Wrongful Death, she wrote about Elliot’s death following surgery in 1991.

Gilbert is survived by her three children, Roger, Katherine, and Susanna, and her partner Dick Frieden.