When Melbourne journalist Andrew Rule was approached late last year to write a biography of superstar racehorse Winx, he “leapt at the chance,” Rule tells The New Daily.

“I knew something about her, having gone to each Cox Plate she had won and taking notice of her,” he says.

“I had, in fact, backed her in the 2015 Cox Plate, her first one. She intrigued me and I wanted to know more.”

Best known for true-crime books, including his Underbelly series, the Walkley Award-winner, who’s also penned a 2014 biography of media mogul Kerry Stokes, wasn’t fazed that his latest subject has four legs.

“Oddly enough, it’s not that different from writing about a human subject,” says Rule of Winx: The Authorised Biography.

“In each case you seek out those witnesses who can help flesh out the picture. In this case it’s a picture of a horse – but the same applies to the trainer [Chris Waller] and jockey [Hugh Bowman]. Inside observers are valuable to the would-be biographer.”

A lifelong fascination with his material also made Rule, who grew up on a farm in eastern Victoria, the right scribe to tell the story of the world-champion racehorse. “I learned to ride around the time I learned to read,” says Rule, who went on to compete in gymkhanas and “ride in a few amateur races at picnic race meetings.”

Yet never, of course, had he come across a horse like Winx.

“She is a freak of nature. To find one like her is like winning a lottery with hundreds of thousands of tickets. She is one of around 20,000 foals born in her season in Australasia – then there are the ones born in the years immediately before and after her.

“Then there are the cream of the imported horses that represent the best of the rest in the world. So, it’s massive odds against any one of them being as dominant as Winx.”

What is it, specifically, that makes her so extraordinary?

“Probably a blend of heart and lung size, the geometry of her legs and her soundness of wind, limb and appetite,” he says.

“She has never looked like breaking down, apart from small injuries that did not harm her. And as the Irish bloodstock agent who helped breed her said: ‘She’d eat stones’, which is Irish for, ‘She has an iron constitution and appetite’, a great advantage for a racehorse in training.”

Winx and Hugh Bowman return to scale after winning the 2017 Cox Plate. Photo: Getty

Her bond with her trainer is, “strictly business, in the sense a racehorse is not a pet but an animal that has to be trained like the equine athlete it is, so that diet and exercise and health matter”, says Rule.

“Coming from a dairy farm background, Chris Waller knows a lot about large-scale animal husbandry, and has instincts and knowledge that would have made him a successful agriculturalist or veterinary surgeon– or possibly anything else he chose.”

Waller, he adds, “is a realist – even though he can seem sentimental after a race win.”

With three Cox Plate wins behind her, Winx is well placed to claim her fourth consecutive victory on Saturday. What would the future hold for her then?

“If she wins and pulls up well, she will probably ‘spell’ as usual on the Hermitage farm outside Sydney, then do pre-training and come back into work at Rosehill in the new year ready to make her swan song at the Sydney Autumn Carnival, probably culminating with the Queen Elizabeth Stakes,” predicts Rule.

“If – and it’s a big if – all that happened, it would take her streak past 30 straight wins. Amazing.”

What’s not in doubt is the calibre of a racehorse that’s become a national icon.

“She has transcended racing in the same way that Bradman transcended cricket and Ali transcended boxing,” reflects Rule.

“That makes her the Phar Lap of the modern age, not only the greatest racehorse in Australia but in the world, and one of the greatest of all time.”

Winx: The Authorised Biography, Allen & Unwin, RRP $44.99