The Irishman makes his professional boxing debut on Saturday when he faces Mayweather at Las Vegas' T-Mobile Arena.
He does so as the UFC's greatest asset, but enters a fight that could prove hugely uncompetitive even if it pays him his greatest ever purse.
Saturday's match-up has gradually been building for the past two years as interest grew in the rivalry between the two biggest figures in their respective codes.
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Boxer Floyd Mayweather Jr. arrives at Toshiba Plaza on August 22, 2017 in Las Vegas, Nevada. Mayweather will fight UFC lightweight champion Conor McGregor in a super welterweight boxing match at T-Mobile Arena on August 26 in Las Vegas.

Image credit: Getty Images

However, even though only a year ago a fight between them appeared little more than a fantasy, for McGregor it has almost been part of a grand plan.
As a young, raw, little-known fighter in Ireland he admired Mayweather from afar and was influenced by the American's criticism of MMA.
The 40-year-old has long been the world's leading boxer, significantly before his opponent became a professional a fighter, and McGregor said: "Originally that's what woke me up.
I was a young kid listening to him talk down about the sport that I was dedicating my entire life to. I'm talking years back, me as a kid.
"Then I realised we're a similar weight, that was when he first came on my radar. I said, 'You know what, I'm going to climb up, and I'm going into different disciplines, I will get that fight'.
Throughout time I rose up - I'm a multiple weight champion - and then it turns out he was the one who came to me. Perfect.
McGregor has also insisted a professional boxing coach would have been no use in his fight preparations.
He has sparred with, among others, boxers like the respected Paulie Malignaggi, and under the observation of boxing referee Joe Cortez, but relied on long-term coach John Kavanagh to hone his technique.
When discussing the prospect of McGregor switching to boxing Kavanagh once said they would recruit Paschal Collins, the Dublin-based coach and brother of former Irish world champion Steve, but the 29-year-old said: "I've been boxing my entire life, preparing to fight my entire life.
"Why would I bring in someone when there's this boxing versus MMA type thing anyway? It's not needed.
I've been with my team my whole life. They know every shot I throw, they know my moods, everything, so there was absolutely no need for it. I was very happy with how the camp went, very happy with how it came together.
"It's like Bruce Lee said, we add what is useful and discard what's not, and that's the way the spars have gone. As the final spar approached, all the unnecessary was gone, and it was a cleaner product, the perfect product. Bruce Lee.
"I'm certainly representing the promotion that is the UFC, that's my promotion. As far as MMA versus boxing I'm my own man in there. I'm not representing mixed martial arts, so to speak, I feel I'm superior to it all."
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