In 1990 the poet Robert Bly wrote a runaway American bestseller called Iron John: A Book About Men. Iron John was about the weird, mystical power of the “deep male”. It became a key text in something called the Mythopoetic Men’s Movement, a shared urge for men to retreat into the woods, bare their woad-smeared chests and generally nurture their inner scowling, bearded masculinity.

Naturally this went down well with 1990s American men, who were delighted to discover they were in fact reservoirs of vibrant male “Zeus power” (High five! Brewskis!). But Blyism wasn’t about ruling the boardroom, or sculpting your abs. It was instead concerned with retreat and mud and melancholy, with becoming a kind of brooding fuzz-encrusted bear.

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Iron John isn’t in the gym or on Tinder. He’s out there chewing on pine cones and stinking of earwax, cultivating mystical phallus-power in the privacy of his own primal soul house, probably in Devon or the Cotswolds. “If conditions are right,” Bly wrote, even the most cowed modern male might “find under the water of his soul, an ancient hairy man”.

Right then. A hairy man. A sweaty, frightening hairy man, all “hurricane energy” and strange, tender feelings. Now who does that remind you of in the world of sport? Here’s a clue: he does bare his chest a lot. He’s a little wild and melancholy. And early on Sunday morning he will fight the fearsomely concussive WBC champion Deontay Wilder in Los Angeles, culmination of a three-year cycle of triumph, pain and vilification.

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Yes, it is of course Tyson Fury, British sport’s own Iron John, for whom victory would be a step towards a potential unifying bout with his counterpoint, the buffed, shiny, notably measured Anthony Joshua; and an occasion that would qualify as the single biggest British boxing event of all time.

More than this, and perhaps still a little obscured by his own tender hooligan act, Fury is also on the edge of a genuinely extraordinary story. Plenty of athletes work their way back from a hamstring niggle or a run of poor form. Fury has come back from a place people don’t come back from. Not only the drugs and the going berserk in Magaluf or the ballooning weight, since when he has lost 10 stone, close to the equivalent of giving birth to a fully-formed adult Lionel Messi. But also the period where Fury seemed stuck in a moment, the defeat of Wladimir Klitschko that he’d been planning since he was 14 years old, and which has seemed to overwhelm him at times.

Mainly it’s something else though. Ahead of the Wilder fight BT Sport have produced a watchable, schmaltz-ridden documentary telling the Fury story, with an obvious redemptive arc. Except, as ever Fury doesn’t fit the easy labels. At the soft, fuzzy emotional heart of the film Fury can be seen talking about how he’s doing it all for his family now, it’s all about the kids. The inspirational music swells. The light softens.

And then suddenly he’s talking about death again, relentlessly, describing feelings of such nihilistic desolation you can almost see them slithering around above his head just out of sight, shadows crawling up the walls. “I prayed for death on a daily basis … I woke up and thought why didn’t I die in my sleep … I tried to drink myself to death. I attempted to crash into a bridge one time.”

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This is the most remarkable thing about Fury, who has also in the past three years become, without really seeming to think about it much, a powerful advocate for openness on mental health issues among the kind of men who rarely open up about anything.

He is remarkably popular too, although this will come as a surprise to some. Three years ago Fury was the subject of a mass petition to get him off the BBC Sports Personality of the Year shortlist, a response to some ridiculously retrograde and offensive remarks about the status of women, homosexuality and – of course – the imminent end of the world.

At the time I wrote an article trying to offer some context, pointing out that Fury is a product of a place entirely beyond the mainstream. A small example: around the time of the BBC vote Fury was busy pleading for clemency for his father “Gypsy” John, who had been sentenced to 11 years in prison for gouging another man’s eye out at a car auction after a 12-year feud over a bottle of beer.

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What was surprising was the response to this. I began to get emails, and not the kind of emails you’re thinking of, approving messages from radicalised Nazi adolescents or mad middle-aged men. These were emails from people who seemed to love Fury, to see his rough, painful edges. One worried that Fury shared his own mental illness, part of which is an urge to speak wildly in public. Another said he felt Tyson needed protection from his thoughts, that mass vilification might be genuinely dangerous.

These days Fury gets these letters all the time (“hundreds of them”). People used to boo him when he appeared in public. Now they cheer. On stage in the BT film Fury looks vaguely pleased at this, but also forgetful, preoccupied, concerned only with this strange proselytising mission.

And this is the second thing about Fury. For all the noise and the toxins, there is a cold hard purity to his obsession with his sport, its sculptural brutality, its relentless disciplines. Fury might be a great doughy Iron John lunk but he is also a very skilful boxer, knock-kneed on skinny legs, a huge square upended sofa of an athlete, arms bent out at right angles like forklift truck pistons.

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Some say he’s taking this fight too early, that Wilder will catch him at some point. But Fury has been imagining that steamrollering right hand, planning for it, digging into his own obsession. He is too clever, too wild, too close to the edge to be discounted. Whatever his fate he will remain a divisive, unforgivably brash figure to many. But boxing’s own melancholy Iron John is also a remarkable story, and a reminder of the power of sport to produce something else, light from the most unexpected sources.