Jim Kay looks like one of his own illustrations.

Because he’s gentle and captivating, that is – not because he’s sketchy. The award-winning Harry Potter illustrator is sitting beside me at one end of a long mahogany table, with a mug of tea.

Jim’s illustrated edition of Harry Potter and the Philosopher’s Stone is sitting between us. I run my thumb along its smooth, cold spine and open it at one of my favourite pages: it’s a picture of Hermione Granger in a corridor at Hogwarts.

‘Hermione is completely based on my niece. She’s ever so sweet,’ he says, moving his hands around like they’re a little bit lost without a pencil.

‘To me she is Hermione: studious and slightly, well, not quite aloof, but she tends to tell me off a lot when she sees me. She’s constantly saying I’m not behaving properly, so the character’s exactly right.’

Hermione Granger illustrated by Jim Kay

As someone whose livelihood is words, it had actually never occurred to me that an illustrator might need real people, real objects and real places to draw. It certainly didn’t occur to me that someone like Jim might build a replica model of Hogwarts castle out of cardboard and Plasticine, but we’ll get to that.

First, squint a little at the intricate etchings on the wall and door behind Hermione. Jim has snuck his friends’ names in there amongst others. Every detail is something Jim has seen and collected in sketch books over the years. That’s what fascinates me most; he spends his life plucking images out of what he sees and stores them up for the right illustration.

‘The graffiti was partly inspired by the Tower of London, where prisoners were held in these tiny, dank, miserable cells,’ he says.

‘The one thing they had was time, so they made these beautiful, poignant carvings in the walls. So there’s that, but also I used to live in Harrow and I used to walk past this one wall at a famous boys’ school there every day. The boys had carved their names into the wooden panels over the years, including Lord Byron and Winston Churchill. It was literally just two weeks ago that I found out they actually filmed some of Harry Potter there. I had no idea – to me it was just a wall I liked back in 1992.

‘The door itself is from a lovely old church that I visited once in Suffolk. When you’re travelling around, you make quick notes and think, “I want to use that one day.” It might sit in that sketch book for 10 or 20 years before you use it. Finally, I got the chance to use that door and the graffiti.’

This whole illustrated edition is brimming with bits and pieces of Jim’s life. He’s infused J.K. Rowling’s stories with fragments of his own world and I suddenly want to hear the origin story of every single painted inch. I flick to a picture of Albus Dumbledore wearing purple robes and ask Jim to pick apart the inspiration for me.

‘Dumbledore is based on a friend who lives on the other side of the world,’ he says. ‘He was extremely kind. He’d seen my original sketches and posed in the same positions as those and sent me these wonderful photographs. Then I would wear this sort-of purple, reflective outfit and sit in front of a mirror to get the lighting and shade right.’

Just imagine it. Imagine Jim sitting in a room on his own, dressed as a wizard, trying to fuse his own reflection with photographs of a bearded friend to get Albus Percival Wulfric Brian Dumbledore just right. Then we’ll get to the significance of that praying mantis on the right.

Albus Dumbledore illustrated by Jim Kay

‘I like symbolism in paintings,’ Jim says, and a rogue piece of trivia I didn’t know I knew comes to the front of my mind. The word ‘mantis’ means ‘prophet’ and it’s traditionally supposed to be a symbol of patience, intuition and wisdom.

‘There’s a praying mantis in there because to me Dumbledore is honesty. He’s honest and wise, but there’s always a catch to his honesty because he holds information back, too. Then there are Sherbet Lemons, but that’s just because he likes Sherbet Lemons. He wrote a book on dragon’s blood, so that’s in there too. The vase is a real vase that I saw at the Metropolitan Museum in New York many, many years ago. There’s no real connection there, I’d just seen it and liked it.’

So Jim already knew a Hermione and a Dumbledore in his life. Did he know all of these people before he drew them, I ask, or did he approach strangers?

‘Harry was the last one I found, actually. I spotted him on the London Underground. He was hanging from the tube bars like a monkey and he had his mum with him, so I said, “This might be a bit strange, but your son has a fantastic character.”’

It wasn’t until much later, Jim tells me, that he could tell this little boy and his mother that he was the inspiration for Harry Potter. This book was a highly confidential project at the time, so any strangers Jim used for models had to come on board without knowing who they were playing. A similar thing happened with the real-life man Jim chose to be Hagrid.

‘When I first saw Hagrid, or I should say a guy like Hagrid, walking through town, he was this big, old guy with a beard wearing a heavy metal t-shirt. He looked terrifying but he was actually so sweet. A real gentle giant, like Hagrid. Actually, giants are my favourite thing to draw.’

He swivels the book on the table slightly towards him, finds this image of Hagrid, and swivels it back to me. ‘I love illustrating giants because it makes you as an adult feel like a child again, looking up at someone. When you’re a boy, you spend so much of your life looking up at people. As an adult, I’m looking up at Hagrid in the same sort of way, you’re thinking of Hagrid as a child would think of an adult. I like that.’

Hagrid illustration by Jim Kay

Like the other pictures, this one of Hagrid is a pastiche of things Jim has seen before.

‘There’s a band called the Weird Sisters who play at Hogwarts, so they’re the initials on the scarf he’s wearing. J.K. Rowling said once that Hagrid is almost like a biker and so I thought he might like rock music. There was a caretaker at my school who had on his belt things that children had given him. So I thought it’d be nice for Hagrid to have that. He’s got badges students gave him and that little space monkey on his belt buckle. That buckle, you’ll notice, is as big as his head. That’s the forced perspective I work with for giants. I like the sense of scale and the mass.’

Jim doesn’t just guess at scale, though. He’s more meticulous with his craft than that. Jim builds little models of every character with Plasticine and places them gently in his cardboard Hogwarts so he can test out the way the light hits each one at different times of day. To get Hagrid right, he lined up a set of those little plastic army solider toys to represent the kids at Hogwarts and then built his own Hagrid figurine to the right scale.

‘I arrange them all like they’re in a tiny toy theatre. That helps me,’ he says. ‘You imagine if you were filming it, where you would put the camera. It’s different for every illustrator but I need something tangible in front of me.’

Jim is ‘full-time Harry Potter’ as he puts it – and that’s why he’s been hoarding cardboard tubes and toilet rolls for years. He’s cleared out his attic so he can build a bigger scale Hogwarts there, not that he has the time. He’s got six of the Harry Potter books left to illustrate and each one is all-consuming. Just think of all the characters left for Jim to find among his family, on trains, in the street and in friends’ faces across the world.

Watch our exclusive Jim Kay video where he discusses illustrating the world of Harry Potter:

Harry Potter to Fantastic Beasts