Steeped in Arthurian myth and legend, lyrically written and masterfully pulled off, the Fionavar Tapestry trilogy is one of the classics of modern fantasy literature. This month, it celebrates 30 years since publication. Thirty years in print, with translations into more than 25 foreign languages.

The Canadian author Guy Gavriel Kay looks slightly shifty when he admits to one of his reasons for writing it. “It will sound arrogant, but it’s a 26-year-old’s arrogance, which is a different kind of thing,” he says, a rueful smile almost, but not quite, breaking out. “I was dismayed at how much fantasy was coming out in those days [the 80s] that clearly had not done anything but go to Tolkien, go to The Lord of the Rings and riff on what he’d done. And they weren’t going back and behind to the same roots and myths and legends and origins that he had been inspired by.”

So what did Kay do? “For me, part of what was going on – well, this is the arrogant part – was wanting to say that the roots of the fantastic go behind where everyone seems to be starting and stopping, which is one quite brilliant work written in the 1940s and 50s,” he says, speaking via Skype from his study in the centre of Toronto.

He was only 26. It was quite a calling, to demonstrate to the world of fantasy literature that they were getting it wrong. But Kay had more reason than most for his self-belief. He had spent a year, between 1974 and 1975, in Oxford helping Christopher Tolkien put together The Silmarillion, JRR Tolkien’s history of Middle-earth. It was quite the training ground for “a Canadian prairie boy”, in Kay’s words.

The job had come about through a family connection – Christopher Tolkien’s second wife was Canadian, and the two families knew each other. When Tolkien was made literary executor for his father’s estate, he decided he needed help, and Kay ended up being drafted in.

“It was a massive, massive project,” says Kay. “And he did not want another fully fledged academic working with him. Family privacy, anxiety, ego elements came into it. And at the time he saw the editing process in the classic ‘senior academic working with the bright young graduate student’ way, which is the template for so much academic work.”

Kay won’t talk about the details of the editing process – it’s a “personal decision” – but you get the sense he doesn’t want to be critical or insensitive. Nor, later, when asked about the state of fantasy today, will he “discuss or critique contemporaries”. “Very Canadian of me, I know,” he writes via email – a man who has described himself as “curmudgeonly”, but who floats lightly past any attempt to get him to be so.

Instead, he describes the Silmarillion experience as “amazing in ways that still reverberate”. “I went from being an urban Canadian to the English countryside,” he says. “And the intensity of intellectual effort during that year was an example to myself of how I could absolutely narrow in and focus on something. I had been a lucky student because I hadn’t been a hard-working student. I had found it relatively easy – skated, if you will. That year I couldn’t skate. It demanded a great deal of concentration and focus and I discovered things in myself in that process.”

Putting The Silmarillion together was “quietly exhilarating” – and almost entirely secret. Kay would spend his days in a barn behind a house eight miles from Oxford, either alone or with Christopher, very occasionally with JRR Tolkien’s biographer Humphrey Carpenter. “It was an exhilarating solitary focus for the year,” says Kay. “And I learned a lot about false starts in writing. I mean that in a really serious way. His [Tolkien’s] false starts. You learn that the great works have disastrous botched chapters, that the great writers recognise that they didn’t work. So I was looking at drafts of The Lord of the Rings and rough starts for The Silmarillion and came to realise they don’t spring full-blown, utterly, completely formed in brilliance. They get there with writing and rewriting and drudgery and mistakes, and eventually if you put in the hours and the patience, something good might happen. That was a very, very early lesson for me, looking at the Tolkien materials. That it’s not instantly magnificent. That it’s laboriously so, but it gets there. That was a huge, huge, still important lesson.”

JRR Tolkien in his study at Merton College, Oxford, in 1956. Photograph: Haywood Magee/Getty Images

Kay returned to Canada, took a law degree at the University of Toronto. Then he fled, to a fishing village on the south coast of Crete, where he made his first stab at a novel, a “classic book in the bottom drawer thing” – a picaresque about a North American backpacking in Europe. He went home, was called to the bar, but never practised as a lawyer, instead writing for a Canadian radio series, The Scales of Justice, which dramatised famous Canadian criminal trials. But The Summer Tree, Fionavar’s opening volume, was already percolating.

“I found myself thinking more and more about what had always fascinated me, which is myth and legend and folklore,” he says. “I had been obsessed with the Arthurian legends all my life, and I knew that that would work its way into any trilogy I wrote. I was fascinated by the Eddas, the Norse and Icelandic legends, Odin on the world tree.”

Fantasy, he felt very strongly, was more than just Tolkien. “I wanted to show you could go behind that to the origins, and work in new ways with similar material. That was part of the self-conscious element of why I was doing Fionavar,” he says. “And I felt empowered to do that because of my connection, with working for the Tolkien estate. I felt validation, some authenticity to my making statements like that.”

Enchanted lands … the original cover designs for the trilogy Photograph: Martin Springett/PR

The Summer Tree tells the story of five students at Toronto University who are spirited to Fionavar, first of all worlds, where an ancient evil has been imprisoned for over 1,000 years – and yes, a form of Yggdrasil, the world tree, makes an important appearance. His agent sold the novel to publishers around the world on the basis of just seven chapters.

Kay escaped back to Crete during a winter/spring break from taping the radio series. “I was going to hide from distraction. Because I was completely in doubt as to whether I had the chops and the stamina and the focus to actually write novels – and so, by hiding, by going away as I did, where there were no distractions, I was able to basically go pedal to the metal. I was writing seven days a week to get the earliest books done,” he remembers.

He bought a typewriter in the flea market in Athens. “It had umlauts, and to this day that typewriter, which I used twice, is the reason there are characters with umlauts in their name in Fionavar, because if it’s there to be used you might as well be using it.”

He wrote the second book in the trilogy, The Wandering Fire, in New Zealand – Maori names and myths seep sadly, beautifully into the story of how the friends try to end a lingering winter.

The trilogy made a name for Kay, but having shown there was life beyond Tolkien, the writer moved on. His next novel, the epic, 800-plus-page Tigana (1990), drew on history rather than myth. Kay researched the history of 15th-century Italy to tell the story of the Peninsula of the Palm, where the people of Tigana, cursed by a sorcerer, cannot even say the name of their country for anyone not born there to hear. His agent loved it. His publishers, keen for more of the same, took a look at the first half before he’d finished. They didn’t want it.

“Tigana scared them. And I was disastrously terrified because I was in the middle of the book,” he says. “I knew it was risky, exceptionally risky. It was atypical for what fantasy was doing in the late 1980s; it was a departure from what I’d done before.”

But he finished it, it went to auction, sold for a great deal of money, and meant that Kay could ramp down his work for the crime series (he has written full-time since 1990). “That’s what started my migration away from myth and legend and more towards history as the underpinning of what I do,” he says.

Since then, his novels have followed a similar pattern, though with vastly different subjects. One critic described his work as “history with a quarter-turn to the fantastic” – a phrase Kay loves. A Song for Arbonne (1992) is set in an analogue of medieval Provence; The Lions of Al-Rassan (1995) takes on El Cid and medieval Spain; The Sarantine Mosaic (1998/2000) parallels sixth-century Byzantium. Most recently, Guy has researched – extensively, as he always does – the history of ancient China, to tell his quarter-turn-to-the-fantastic stories Under Heaven (2010) and River of Stars (2013).

Kay has said, many times, that he does this quarter-turn because he doesn’t like using real lives for his fiction. “I’ve been calling it an epidemic of co-opting real lives, to do whatever we want to do with them. And as an artist, for my own process, I have a problem with this. I don’t want to offer the assumption that I know what Abraham Lincoln’s favourite position in bed was,” he says drily. Though he is careful never to criticise any writer who does: “I have vastly enjoyed a great many books that do not share my view on this ... as a reader I can enjoy when people do this, but we separate out in our minds aesthetic and ethical issues. I’m very comfortable reading a brilliant book that uses Thomas Cromwell as a protagonist, and I will call it a brilliant book. I reviewed Bring Up the Bodies – I gave it the best review that I’ve ever given a book.”

He just won’t do it himself. “I’m happier not pretending I know anything about El Cid in Spain,” he says. “He’s a Spanish national hero. I’d rather invent a character inspired by him but clearly not identical to him. And then I feel liberated creatively. I steep myself in a period and then I twist it just that little bit to give myself the ethical and creative space that seems to work for me.”

The change of genre means “there’s still a segment of readership that takes the view they are irked with me for life for leaving Fionavar. That stamped them and imbued them and partly defined them when they were young, and they wanted more of the traditional high fantasy,” he says.

Kay, a recent recipient of the Order of Canada for his “outstanding contributions to the field of speculative fiction” – and an author with sales approaching 3m copies worldwide, according to his publisher – is sanguine. “I’m still proud of the Fionavar Tapestry. The fact I don’t write the same way is as much as anything else the fact a man in his 50s doesn’t write the way a man in his 20s does – or he shouldn’t. We shouldn’t be interested in the same things, we shouldn’t be artistically frozen in amber at the point that we were when we first appeared on the scene. We should evolve. And that’s what it is for me,” he says.

He cites a line from John Fowles’s Daniel Martin: “Ban the green from your life, and what are you left with?” “I love that line. To me what that’s saying is: if you feel embarrassed of, or regretful of, or close your eyes when you look at what you did artistically, or romantically, or pharmacologically when you were 24 years old, what are you left with and what constitutes you? That green in your life is where you started; it’s your origins story, and I don’t ever want to ban the green from my life.”