Heavyweights are not supposed to be laid-back – unless they have walked on to a left hook. But Anthony Joshua, elegant in his black, tailored tracksuit, embroidered with his “AJBxng” motif, his massive fists housed inside designer gloves and an initialled baseball cap perched on his head, is almost spookily relaxed, oozing menace and low-key glamour in equal measure.

At the Principality Stadium in Cardiff a week on Saturday, as many as 80,000 fans will hope to witness their world heavyweight champion throw off his languid mien and explode into life to knock out the unbeaten New Zealander, Joseph Parker – who owns the WBO’s slice of the championship – and continue his glorious ascent to sporting sainthood. Joshua knows it will not be that easy.

Nor is he concerned. Speaking on Wednesday at the English Institute of Sport in Sheffield – where he learned his craft as an amateur a decade ago with the national team director of coaching, Robert McCracken, who guides him still – Joshua says history is for others to write. His job is to deliver the detail.

“Do people know about history?” he asked rhetorically. “I think people just see it as a unification fight. But in terms of stats and facts it’s massive. Are you guys going to tell the world how great it is? That is what is important. People who really study or watch boxing know how big a fight this is; that’s why Parker is taking it deadly serious – and so am I. It’s big news for this current time in the heavyweight division.”

Ten of Joshua’s 20 fights – all stoppage victories – in five years as a professional have been for titles of varying importance – and lately they have had the stamp of the alphabet boys: the WBA, IBF, WBO and, for what it’s worth, the IBO; the last three of his championship bouts have been in front of 80,000-plus paying spectators, with millions more providing the pay-per-view revenue that makes it possible for Sky to show them in the first place.

Joshua is used to expectations but he is a stadium fighter now and for the rest of his career – or until someone reminds him how precarious the heavyweight business can be. Yet he regards himself as an ingénu – “just three stadium fights”, as he describes it. Only Carl Froch and George Groves in recent times among British fighters have played to such huge audiences.

Was that an echo of complacency? Joshua is aware of the dangers of his business, having spent time on the canvas against Wladimir Klitschko at Wembley Stadium last April, before rising to end the Ukrainian’s illustrious career with an irresistible onslaught in the penultimate round. He knows Parker could put him there again – although he is equally certain he will prevail.

“He doesn’t throw many combination punches but he throws more [than Deontay Wilder, who will be ringside],” Joshua says. “There has never been one champion in the heavyweight division who relied solely on power and one punch. Parker has a bit more all-round game than Wilder. When you talk about Parker, you talk about his speed, his stamina. He’s got a good chin. There are more stats and facts than he just has a right hand [like Wilder]. That is what makes it a dangerous fight.”

Would he have given him a chance against Klitschko, though?

“I don’t think I’d have given many fighters a chance against Klitschko. Remember, when I fought Klitschko, he didn’t say he was just in great physical condition, he said he was obsessed. His mind was in the right frame that night. I don’t think many people would have beaten him. When a man is obsessed, he is in a tough place to be.”

Wilder remains the menacing giant in the alleyway. It is the fight everyone wants to see: two unbeaten knockout monsters. He struggled briefly against Luis Ortiz, the aged but accomplished Cuban, in his last fight but kept his stoppage run going.

“When he won, I just thought: he’s supposed to do that, he turned pro after the 2009 Olympics. After nine years as a pro you’re supposed to beat Ortiz. It was his 40th fight. I thought: by my 40th fight no one should be giving me problems. By my 40th fight, I should be a seasoned professional.”

And by his 40th fight he will probably have made more history than he ever could have imagined.