When Irish author Eoin Colfer decided to write a children's book about a 12-year-old criminal mastermind, he did not think it would go down well at all.
His first book, Benny And Omar (1998), had been criticised in the media because its protagonist, a normal kid who sometimes misbehaves, was "not a good role model".
Colfer's next creation was the complete antithesis of a role model: Artemis Fowl, an utterly amoral child prodigy who, upon discovering that fairies exist, decides to kidnap one for ransom.
"I thought, I'm going to get awful press and terrible reviews because he's just a really bad person," recalls the 54-year-old over the telephone. "And then it became hugely popular and I was hugely surprised."
Colfer, who had previously sold books only in Ireland and occasionally in Germany, found himself holding the reins of a best-selling franchise, often described as "Die Hard with fairies", that would go on to sell more than 25 million books around the world.
"I think people sometimes enjoy reading about the bad guy," he muses, "so long as he develops a conscience, which Artemis does in the end."
Colfer began the Artemis Fowl series in 2001 and wrapped it up eight books later in 2012 with The Last Guardian. He went on hiatus for the next seven years, during which he dabbled in other kinds of writing, but is now back with a follow-up, The Fowl Twins, about Artemis' younger brothers, as well as his first adult fantasy novel, Highfire.
An Artemis Fowl movie that has been in the works for nearly 20 years will finally hit the screens in May this year, directed by Kenneth Branagh.
"It's just so surreal," says Colfer. "It's a really nice bonus in my career and I've had a wonderful career."
The Fowl books, while for children, always had something of an adult edge to them - the humour is often scatological and a recurring character is a kleptomaniac dwarf with deadly flatulence.
People have said to them, 'You know, your dad's been writing about you,' and they're like, 'Yeah, well, we probably won't read it anyway.' They're not that concerned about what their dad does. ''
AUTHOR EOIN COLFER on his sons, Sean, a teenager, and Finn, who is in his early 20s. The Fowl Twins is based on the siblings
In Highfire, Colfer gets to let loose with all the non-PG-rated material that would never have passed muster in the Fowl series.
He had intended to write a children's book to begin with, he says, about an old man who lives alone in the countryside, having been traumatised in some way, and who strikes up a friendship with a juvenile delinquent.
"Something kept saying to me, this is not right," he recalls. "So then I thought, maybe it's a creature of some kind. And then the idea of a dragon came up. And then he got grumpier and started drinking a bit too much and his language wasn't very nice. So I knew it had to be adult."
Highfire, which has had its screen rights picked up by MGM Television, features a dragon called Vern, short for Wyvern. He is a little over 2m tall and the last of his kind. He lives as a recluse in a swamp near New Orleans, drinks far too much vodka and is obsessed with the movie Flashdance.
"He's more like Homer Simpson (from The Simpsons cartoon) than anything you see in (fantasy TV series) Game Of Thrones," says Colfer.
Vern's secretive existence is disrupted by Squib Moreau, a halfCajun teenager whom Colfer describes as the "spiritual descendant of Huckleberry Finn", a vagabond youth created by author Mark Twain. Squib stumbles across Vern's lair while fleeing a corrupt sheriff whom he witnessed committing murder.
Colfer took inspiration from the Honey Island Swamp monster of Louisiana folklore, which legend tells was spawned after a train with a travelling circus on board crashed into the swamp, whereupon some chimpanzees escaped and interbred with the local alligator population.
Artemis Fowl's early readers would now be adults, and Colfer hopes they will return to pick up Highfire. He meets many such grown-up fans at his events, he says, and some even bring their children, whom they have got started on the Fowl books. "You see generations of Artemis Fowl fans coming along," he says. "That's so nice."
Colfer, a former primary school teacher, developed a fascination with storytelling at a young age because of the Viking Age stories he learnt in history class.
One story that stuck with him was when his father, also a teacher, told him that buried beneath the main street of their village in Wexford, Ireland, was a Viking street, perhaps even an entire village. This would later give him the idea for the underground fairy civilisation in the Fowl books, in which the fairy folk have developed advanced technology to help them hide from humans.
After The Last Guardian, Colfer decided to take a break from Artemis Fowl. In the interim, he wrote in other genres, including some crime thrillers, a 2016 Marvel novel called Iron Man: The Gauntlet and a play, Holy Mary, which opens in May at the Theatre Royal Waterford in Ireland.
He had written the first few chapters of The Fowl Twins early on, but put them aside and reread them only 21/2 years ago. "I got very excited by them. And when I felt that excitement, I knew that my brain was ready to go back to the world of Artemis Fowl."
The Fowl twins, intelligent Myles and impulsive Beckett, are based on his own sons, Sean and Finn, whom Colfer says remain immune to their father's celebrity status in children's fiction. "People have said to them, 'You know, your dad's been writing about you,' and they're like, 'Yeah, well, we probably won't read it anyway.'
"They're not that concerned about what their dad does. That's quite normal, that you don't think what your dad does is very interesting."
He was an extra in the Artemis Fowl film, though he declines to say what role he plays in case it gets cut from the final product. "I realised I'm not good at being an actor. I don't have enough patience to do something 10 or 15 times."
Branagh cast British dame Judi Dench as Root, a fairy police commander who in the books is male and at times sexist towards Holly Short, the young female captain whom Artemis kidnaps. The gender-swop has been controversial among fans, but Colfer is full of praise.
"I wondered how they were going to approach it," he says. "So they showed me some footage and after two minutes, it just seemed she was born to play the role, because she's not playing my version of Root, she's playing her own interpretation. And she interpreted it wonderfully. She's fantastic."
He adds: "It's lovely to be back in this world. Now I'd like to do different projects and explore different areas of my imagination, but the only reason I can do that is because of Artemis. So hopefully this movie's a success. People will go back and read the books again.
• This article includes affiliate links. When you buy through affiliate links in the article, we may earn a small commission.