Author of the Inkheart Trilogy

I love and adore the books because my children grew up with them. Neville is my favourite character – I love that JK Rowling shows him as the boy that has been through such terrible things and comes out such a beautiful human being. I’m so impressed by how bold she is at addressing very dark themes in children’s books – torture and loss, for example – and does it in such a brilliant way that they can cope with it. I always think this is the biggest task you have when you talk with children: to show them the darkness in the world and give them ways to look at it.

Harry Potter also gives you the concept that friendship can overcome evil. I love that she has no lonely hero, she believes in several heroes working together. There is a way that JK Rowling interprets this world – because Harry Potter is about our world – that is perceived by adults and children as something they want to see themselves. I still see my 26-year-old daughter reading them over and over again and that is such a magical thing. JK Rowling brought storytelling back.

Cornelia Funke: ‘She’s so bold at addressing very dark themes.’ Photograph: Jane Bown

Fly By Night, The Lie Tree

I’m very much aware that JK Rowling has done me nothing but good: her success showed publishers there was a huge market waiting for the right children’s book and encouraged them to invest in children’s authors. If that hadn’t been the case, I might not have been able to write full time for the last 10 years.

The Harry Potter series helped to open up the crossover market, letting adult readers overcome their preconceptions and self-consciousness about reading children’s fiction and allowing those books to find a wider audience.

Last but not least, I really enjoyed the books! I respect the way that JK Rowling didn’t play safe with her winning formula, but continued taking risks with the format, letting the series deepen and darken as it went on.

When Harry Potter and the Half-Blood Prince came out, my partner and I pounced on the first copy we could find, even though we were backpacking through south-east Asia at the time, and thus had to carry the hefty great thing in a rucksack. No regrets...

Frances Hardinge: ‘She continued taking risks.’ Photograph: Frantzesco Kangaris/The Guardian

The Ottoline Books

When the first Harry Potter book came out, I was working with Paul Stewart on a fantasy series for children called The Edge Chronicles. Every time a new Harry Potter book was published, we saw a bump in our sales.

Then there was a three-year gap between the fourth and fifth books, and as people were waiting, our sales went through the roof. JK Rowling enthused readers; she has been hugely beneficial to our reading culture.

The books are so rich. I love their iconography, the characteristics of the different school houses and the education policy emanating from the Ministry of Magic. The details are fantastic and so easy to visualise. Dumbledore is one of the world’s great characters. He’s complex and wise. He would make a brilliant minister for education.

As an illustrator, I was always sad that one of the greatest children’s books didn’t have illustrations. Now a friend of mine, Jim Kay, has just illustrated the first two Harry Potter books and is on a rolling mission to do the others.

Chris Riddell: ‘Every time a new Harry Potter was published, we saw a bump in our sales.’ Photograph: Lauren Hurley/PA

Millions, The Astounding Broccoli Boy

Harry Potter is a cultural phenomenon on the scale of Star Wars or the Marvel universe. But behind the money and manpower of the franchise is the power and integrity of one woman, alone with a pen. Even the longest books in the middle of the series feel necessary and you still want to read them; JK Rowling always knew where she was taking us.

For example, the throwaway incident of the snake in the zoo in book one turns out to be the crux of book seven. A generation encountered that snake in childhood and discovered its meaning on the brink of adulthood.

I watched Harry Potter’s rise in popularity through my second son. There was no hype at first – he read the first one in paperback and stumbled across the second on holiday. By the time book three came out, he was queuing at midnight outside the bookshop.

Despite its success, I don’t think the world of children’s fiction has changed massively since Harry Potter – apart from the assumption that you must be phenomenally wealthy to write it.

Frank Cottrell Boyce: ‘Behind the franchise is the power of one woman, alone with a pen.’ Photograph: Alamy

The Horrid Henry Books, The Monstrous Child

I was lucky enough to read the first Harry Potter when it was just a book, like any other. Later, with all the hype, that became more difficult. The first is still my favourite. It’s so funny – the letter addressed to Harry under the stairs made me laugh a lot.

Children’s authors owe JK Rowling a huge debt of thanks. I used to get asked all the time: “Does she take all the publicity?” But there was no publicity for children’s authors before Harry Potter. Children’s books were left off the bestseller lists.

Harry Potter broke a lot of publishing rules. One reason JK Rowling had a hard time getting her book published was that it was too long for the eight to 12 age group. She proved that children of that age group loved reading longer books, so the rules loosened.

The fairytale aspect of the Dursleys [standing in for] Harry’s parents is very clever. It’s the fantasy of your real parents being dramatic, amazing people, instead of the dull couple in the suburbs you happen to live with.