I first read Philip Pullman’s His Dark Materials trilogy as a young teen; it felt like a revelation. The books had a rough-textured animal-breath closeness that I had rarely encountered before, and at the heart of that was a small child, swift witted and loose handed with the truth, throwing mud at rival children, and her soul companion, her daemon Pantalaimon. I decided there and then, with all acknowledgements to the glory and joy of Alice’s Adventures in Wonderland, of Sophie in Diana Wynne Jones’s Howl’s Moving Castle, of Malorie Blackman’s Sephy Hadley in Noughts & Crosses and of Roald Dahl’s Matilda, that the greatest heroine in British children’s books was Lyra.

There is good evidence that many people of my generation felt the same. Pullman now shares with Shakespeare, Jonathan Swift and Philip Sidney the distinction of having popularised an English-language name that is now part of the lexicon. We owe the name Vanessa to Swift, who gave it as a piglatinish nickname to his lover Esther (Esse for short) Vanhomrigh, and Pamela (pronounced, originally, Pameela) to Sidney. Shakespeare has at least two; the first sighting we have of Miranda (from mirandus, meaning wonderful) is The Tempest, and Jessica, probably in an Anglicisation of the Old Testament Hebrew name Iscah, first appears in English in The Merchant of Venice. And last year, 362 new Lyras were born.

The name came, originally, from a misunderstanding. Pullman told the New Yorker: “There was a hymn I particularly liked called ‘Jesus Christ Is Risen Today, Alleluia’ … And under the number of the hymn, printed in small italics, was usually the name of the author. In this case, the name there was Lyra Davidica.” It was, he thought, a good name. “In fact, what Lyra Davidica means is the ‘harp of David’. ‘Lyra’ is a Greek word for a musical instrument like a harp.”

Where did Lyra herself come from? She has, I think, DNA from many places: from the tricksters in old English ballads, from William Brown and his Outlaws, from the orphaned Cinderella (not the Disney one; the versions from the 17th and 18th centuries, who had wit and guile and an edge of ruthlessness on their side. In Giambattista Basile’s La Gatta Cenerentola, Zezolla murders her stepmother by chopping off her head with the lid of a trunk.) Pullman told me: “Lyra just came to me as she was. I didn’t change a bit, or alter anything to her advantage. Having taught in middle schools for 12 years or so, I was well aware that there was a Lyra in every class. The point I always make, when asked about it, is that Lyra is not special. She’s ordinary, not to say common. But it’s the qualities she shares with so many real girls that help her when she finds herself in extraordinary circumstances.”

Lyra has nothing in her that makes her uniquely suited for her task ahead. She is made, not born, a hero

So Lyra is in some ways utterly commonplace: solid legged, dirty nailed, a liar without much concern about the consequences of her lies. That ordinariness is what makes her so vivid; despite the fact that the witches have a prophecy about her, she doesn’t have, unlike Harry Potter, any particular magic: she has nothing in her that makes her uniquely suited for her task ahead. She is made, not born, a hero. As Pullman says, “I’m an old-fashioned existentialist in some ways: existence precedes essence, and I’ll fight anyone who says different.” It takes work, the books tell us, to become a heroine: strenuous effort, constant attention to the world, a willingness to peel back the layers of your own heart.

But of course she is also not ordinary, because she has in her possession a compass-like device that can tell the truth, one of the loveliest inventions of children’s fiction, alongside Tolkien’s ring and Rowling’s pensieve: an alethiometer (from the Greek aletheia, truth). Her ability to read it gives her, in the world of the book, an extraordinary authority that most children are denied. She is able to transcend that one factor of childhood that I found hardest to bear: the sense of disfranchisement from a world that extends so far beyond your understanding as to be painfully opaque. I read with a fierce hunger to see the world; I hated, above everything, not understanding.

‘It takes work to be a heroine’ … Lyra with her daemon Pantalaimon. Photograph: BBC/Bad Wolf/HBO

I think a true hero or heroine needs to have both something we want or covet (for instance, a princedom in Denmark; a fairy godmother) and something that we are (tormented by our own uncertainties; transformable). Lyra has both in Pantalaimon. The daemons – animal manifestations of the human soul – are the reason the books pulse with life: they have, after all, twice the usual amount of life in them. I am often asked, by children I meet at school visits or book festivals, what would be my daemon? It became to a whole generation of readers a kind of taxonomy of self-definition (I think mine would be something that seeks to be up high: a squirrel, or a bird of the less glossy kind. Be wary of people who say “a leopard”: they do not know themselves.)

The thing I wanted most, though, changed over the course of the books. By The Amber Spyglass, the final book in the trilogy, what I wanted was not the alethiometer, nor even a daemon, but the love. Lyra falls in love with Will Parry, and finds herself stunned. Their love is physically felt: “I want to kiss you and lie down with you and wake up with you every day of my life till I die.” Sexuality, and the adult love that comes with it, is in Pullman’s world something to cherish: something, seen in its true light, more astonishing and surprising even than riding over snow on an armoured bear. Pullman said in an interview a few years ago that, if the book is a version of Paradise Lost, “what I wanted to do was represent the fall as entirely good. It is good for people to know things, to grow up, to become sexual beings.”

And Lyra’s love allows her a different kind of seeing: it is the transformative vision of her love that allows her – without giving away the plot – to save Pullman’s world. That is, perhaps, the final reason Lyra has been so loved: she is in part Pullman’s longhand philosophical proof of an argument at the heart of all three books of the trilogy: notice. Lyra and Pan’s eyes are everywhere. She is curious above everything. It is the core demand of the books: pay loving attention to the world. We owe the world our ferocious attention, to fail at that would be the true fall.

I’ve been writing children’s books for more than a decade now; when I go to speak at schools, irrespective of country, the children’s questions are often the same. (“Where do you get your ideas from? Do you ever get stuck? How much money do you make? Do you write with a pen?” These all seem entirely fair questions to me, and in fact are what I long to ask other writers.) But recently at a festival in Italy, I met a more than usually philosophical group of 12 year olds. They asked: “What is the colour of happiness?” and “What one thing would you change about your life?” – like being interviewed by a gang of small, glitterpen wielding Kierkegaards. The last question was, “What is it you are trying to do when you write?” and I thought of His Dark Materials. As a child those books felt to me like food. So what I am trying to do is informed profoundly by that: I want to build stories that feel like nourishment. His Dark Materials stands as a testament to what children’s books can be: three books that add up to a feast.

• His Dark Materials begins on BBC1 at 8pm on 3 November. Katherine Rundell’s most recent book for children, The Good Thieves (Bloomsbury), is out now.

• This article was amended on 11 November 2019. An earlier version stated incorrectly that Philip Pullman had “invented” the name Lyra. The text has been changed to clarify that his books have helped popularise the name.