In terms of epic battles, it's hardly up there with Harry Potter's struggle against the evil forces of He Who Shall Not Be Named. But millionaire author JK Rowling's court case this week against a small US publisher and its unauthorised A-Z guide to the boy wizard's universe has refocused attention yet again on the cross-cultural, trans-generational phenomenon that is Harry Potter.

The 42-year-old writer flew to New York especially on Tuesday to make her case against the publication of The Harry Potter Lexicon, a 400-page guide to the seven-book series compiled by a former librarian and Potter obsessive, Steve Vander Ark, which was to be released by Michigan publisher RDR Books.

In an emotional testimony, Joanne Rowling -- who adopted the androgynous pen-name JK so as not to alienate young male readers -- argued that the Lexicon infringed upon her intellectual property rights and copyright, and that large portions of the text are lifted almost verbatim (and unattributed) from her own work. It would also spoil her plans to release her own Potterpedia to raise money for charity.

"I believe this book constitutes wholesale theft of 17 years of my hard work," she told the court. "It adds little if anything by way of commentary; the quality of that commentary is derisory; and it debases what I worked so hard to create."

Anyone following the case could quickly conclude that it's not about money. Why would it be when Rowling is worth somewhere in the region of E678 million? The author was fighting back tears as she spoke of her love for the characters that she spent almost two decades developing, and how they "saved" her financially and, more importantly, psychologically.

"These characters meant so much to me, and continue to mean so much to me, over such a long period of time," she said. "The closest I can come is to say to someone, 'How do you feel about your child?'."

That Rowling is so emotionally involved with the novels and the characters goes some way to explaining the lasting popularity of Harry Potter. The numbers speak for themselves. The seven books in the series have sold 400 million copies worldwide (the top four fastest-selling books in history are all Potter novels).

Meanwhile the five movie adaptations, which have made stars (and millionaires) of their young cast -- Daniel Radcliffe, Emma Watson and Rupert Grint, have grossed some E2.8 billion to date globally (the next cinematic instalment, Harry Potter and the Half Blood Prince, is due next year, while the final adaptation, The Deathly Hallows, will be released in two parts in 2010 and 2011).

All together, the Harry Potter industry is valued at almost E10 billion -- not too shabby considering the whole enterprise was conceived by a struggling single mother while on a delayed train journey, who proceeded to write the first instalment sitting in cafes around Edinburgh.

But those record-breaking statistics only reveal one facet of the Potter craze. Trying to distil the essence of the novels' enduring appeal has proved more difficult for many mere Muggles. The first novel, Harry Potter and the Philosopher's Stone, came out in 1997, and for the next decade, the six sequels continued to draw in millions of young fans in an age when reading seemed to be a dying pastime that was losing ground to ever-elaborate game consoles, computers and DVDs.

So what hooked all those young -- and indeed not so young -- readers? (Even the defendant Vander Ark wept when he came face-to-face with his idol Rowling). Technically, Rowling is a supreme storyteller whose meticulous sense of plotting, breadth of imagination and unpretentious writing style made the books accessible to all ages and levels of readership.

Over the course of seven books and 4,100 pages, Rowling was able to craft a coming-of-age epic that synchronised with many of her young fans' own passage into adulthood. The books united readers from all backgrounds and age groups (with the exception of the Catholic hierarchy who condemned the books' apparent promotion of magic) to the extent that each new increasingly extravagant book launch became a massive pop culture event, complete with midnight book parties, fancy dress celebrations and pan-global reading marathons.

Of course, readers were swept up by the fantastical adventures of Harry and his magical Hogwarts school pals, but what started out as an episodic, light-hearted and kiddie-friendly series soon took a dramatic turn into much darker territory in its latter novels. The tomes became longer, bleaker, sadder and more demanding -- and yet still spellbound readers couldn't get enough.

Many critics have argued -- convincingly -- that Rowling is a realist writer, despite the magical leanings of her tales. The first novel was written out of Rowling's devastation at losing her own mother to MS, and death and loss cast a long and defining shadow over the Potter series.

Rowling was never afraid to confront difficult and uncomfortable themes like these, and children responded overwhelmingly to her non-condescending and frank style (something which renders even more puzzling Rowling's decision to out Professor Dumbledore as a homosexual only after the series was completed and not during it).

The final three books, which were released in 2003, 2005 and 2007 respectively, are also very much of their time: bloody, wrenching and preoccupied by war. In many ways, Rowling transmuted the horrors and uncertainties of the post-9/11 world into a form that children could understand, and they liked the books all the more for it.

But throughout all seven books, Rowling never lost sight of the timeless themes that will always appeal to the human imagination: the joys and costs of friendship and loyalty; the pain of loss; the search for a place to call home; and the struggle to find yourself.

Since wrapping up the Potter series last year (and being named Entertainment Weekly's Entertainer of the Year and Time magazine's runner-up Person of the Year), Rowling has said she's planning two books -- one for kids, and one for adults. She's hinted ever so gingerly that she may resurrect Harry Potter for an eighth instalment, and we can be sure that if Rowling does return to Hogwarts some day, she will still have that magic hold over the young and the young at heart. That's one power she will never have to go to court to protect.

- Declan Cashin