Conor McGregor is now so rich and famous that he doesn’t have to roll out of bed before two o’clock on any hot August afternoon in Las Vegas. This past weekend, laced with heavy spending and partying, a 3pm Sunday interview was far too early for the Irish fighter and new sensation of UFC, the booming business of mixed martial arts. McGregor could only be roused at four after he had celebrated his girlfriend’s birthday on Saturday in a style which suits the lavishly-bearded, sharp-suited, big-talking world champion.

“I’ve become accustomed to this life,” McGregor says when we finally start talking while he takes an hour-long drive up and down the Vegas Strip, his new playground and battle arena. “I love what I do and I’m extremely grateful. This weekend has been very good. We got a nice suite overlooking the Strip, at the Cosmopolitan. And we went shopping for 10 hours straight yesterday. I got us a limo and we stuffed it with shopping bags so it was a great day and then we had a great night.”

A 90-minute wait for McGregor is not that surprising, especially from a media phenomenon who calls himself ‘The Notorious’ and was barely known outside his old Dublin neighbourhood of Crumlin two-and-a-half years ago. McGregor once worked as a trainee plumber. Now he is such a huge star that 70,000 people applied for tickets to attend his press conference in Dublin this year.

Most of Ireland’s World Cup rugby squad also got up at the dead of night to watch and whoop, led by the normally unflappable Jonny Sexton and Conor Murray, when McGregor became the UFC’s featherweight champion last month after he fulfilled his usual prediction and knocked out Chad Mendes in the second round.

Before the fight, at the MGM Grand, 11,500 fans squeezed into a crammed arena to watch McGregor’s weigh-in. Sinead O’Connor then sang live to accompany McGregor’s walk to the cage where he completed his crushing victory over Mendes. His next fight, against José Aldo in a unification contest, will be another record-breaking event that the UFC could stage at the Dallas Cowboys’ 85,000-seat stadium.

“It’s absolutely insane,” McGregor says as we reflect on his anonymity when, in early 2013, he was still claiming benefits in Dublin before his first UFC contract. “Who has climbed to the pinnacle of the fight game like this? Nobody from Ireland. And to do it in the time I’ve done it, so quick? It’s mind-blowing. But I never forget the struggles. I never forget where I came from. I never ever forget the hard times. I pinch myself because I am surrounded by luxury. But make no mistake – it’s luxury built on sacrifice.”

McGregor remembers being lost at 17 and on a desolate road to becoming a plumber. His parents had moved the family out of Crumlin to a better part of Dublin but McGregor resented the move. “I never truly left Crumlin. You have your friends at that age and where we moved to I didn’t relate to anyone. My boxing gym was in Crumlin, my football club was in Crumlin. I love Crumlin dearly. I love Dublin 12 dearly. Anytime I am back in Dublin I head to Crumlin, to my friends. I’ve had many great moments – but to go back this month to Crumlin as the UFC world champion will be the pinnacle.”

Moving from Crumlin coincided with his mum’s grand plumbing plan. “It just wasn’t for me,” he says of life as an apprentice plumber. “I was waking at 5am and walking in the dark, freezing cold until I reached the motorway and waited for a guy I didn’t even know to take me to the site, where I worked for 12 hours and then got driven back and walked home. I know there are passionate, skilled plumbers. But I had no love for plumbing.

“After school you go to college or get a trade. You don’t sit around doing nothing. My parents dragged me out of bed but I was unsure what I wanted to do. Then my mother found me this place in the plumbing industry. It’s weird how society works. Rather than allowing you time to find the thing you love and can pursue with complete conviction, we’re told: ‘You must work – no matter how much you dislike it.’ I just felt I was going to be the person I wanted to be, regardless of what anyone said.”

McGregor told his parents that his plumbing career was over and, to their confusion, promised he would become a UFC world champion. “When I got into combat sports it was to defend myself. I just started out with a love of learning how to fight, mastering defence and attack. Then the UFC came to Dublin [in 2009] and I saw the machine in full flow. I thought: ‘There’s a place I can make a good living’. I saw all the fans and fighters and I didn’t see me. I was different. I knew people would love that. So it started with a love for the sport and it’s been strengthened by a love for the money it brings.”

His professional MMA career began as a cage fighter in March 2008 – when he was only 19. He won his first bout at an event called Cage of Truth 2 in Dublin. He lost twice as a young pro but then a nine-fight winning streak, coupled with his outrageous capacity for promotional hype, won him his first UFC contract in early 2013. McGregor’s subsequent rise has been astonishing. He is the smartest trash-talker and savviest self-publicist in the business. And he can fight. Against Mendes he overcame his opponent’s prowess as a wrestler to knock him out.

“It amuses me how many so-called experts claim he won the first round. He was done in the first round. He was breathing heavily and I attacked his body relentlessly. I had him badly hurt even before he got the takedown. In a fight to the death what does a takedown mean? In the jungle a lion knows he must attack the neck. It’s the same in my game. You have to attack the neck, the chin. These guys who try to win by getting someone in an arm or leg-lock to force a submission? That’s not being victorious. I believe in the KO.

“The second round he came out again and I caught him with heavy shots. He secured a second takedown but I rolled out of it. I got to my feet and went back to work. I went to the body and I lit him up. You then attack the neck and the chin. That’s how you kill the fight.”

Mike Tyson and Arnold Schwarzenegger tweeted ecstatically from cage-side. McGregor was gratified, especially in the glow of Tyson’s praise, but he was most affected by the appearance of his mother in the Octagon [the steel cage where MMA fights are held]. He later tweeted a photo of his mum hugging him, with the message “Done it, Ma!”

Weeks later the emotion spills out of him. “She had never been inside the Octagon and my coach, John Kavanagh, made sure she was there. Many years ago my mother rang John when I was drifting. John came to the house and got me back on track. That night he told my mother: ‘When Conor wins the world title I will bring you inside the Octagon’. That promise was fulfilled. My mother has done so much for me. I can’t even put into words how much I love her. I miss her and my father dearly. I cannot wait to go home and have some good nights and good meals with them.

“It’s hard for them when I go in the cage. They endure their own emotional struggles. It’s a very intense experience – the purest form of adrenaline and excitement. I’m addicted to it. There is so much else in this game – so much business, so much media, so much work.

“But when I make that walk, and when my feet touch the Octagon floor, it takes everything away. To be completely in that moment is like nothing else on earth. I wish I could just show up and get that feeling – and then be with my people. But you have to do all the other stuff.”

Bang on cue, a fan waves deliriously at McGregor on the Strip. The Irish fighter rolls down his window. “What’s up buddy? How are you? Where are you from?”

“Brazil,” says the bug-eyed fan. McGregor yelps in delight, thinking of his next opponent, Aldo, who is also Brazilian. “Woooohh! José Aldo! Are you Team Aldo or Team McGregor?’

“José,” says the fan, apologetically, “but I watch you.”

“I’m only joking, man,” McGregor grins before posing for the obligatory selfie. As the car picks up speed, McGregor yells: “Tell José I’m coming!”

The fighter is ominously quiet when I suggest that, for all his mockery of Aldo, who withdrew from their showdown last month through injury, to be replaced by Mendes, he surely respects the Brazilian? “I don’t know him,” he eventually says. “The only way I would gain respect is through battle. He has been around a long time and done some good things. But he didn’t show up. He and his team were watching my fight from under their duvet, praying that Mendes would win so he wouldn’t have to fight me. How can I respect that?

“But if he does show up, in Dallas or Vegas, in December or January, it’s going to be big. It always is if McGregor’s on the card. I’ll unify these belts and then next summer we’ll go to Croke Park in Dublin. I’d be very surprised if it takes 10 minutes to sell 82,000 tickets for Croke Park. So many [Irish fans] were in Vegas, with the 11,500 at the weigh-in for Mendes. It was historic. Looking at those pictures from the weigh-in was like looking at something from Gladiator and the Roman times. I’m blown away.”

Conor McGregor punches Chad Mendes in their UFC interim featherweight title fight inside MGM Grand Garden Arena in July in Las Vegas. Photograph: Josh Hedges/Zuffa LLC via Getty Images

One of the UFC’s intriguing quirks is that, alongside McGregor, such a macho sport’s biggest star is a woman – Ronda Rousey, who has challenged Floyd Mayweather. McGregor lauds Rousey and says: “I’d also jump in and box Mayweather. 100%. What do you think would happen?”

If they fought as traditional boxers, Mayweather would outclass McGregor with his sublime technique. “Yeah,” McGregor says, “but in a real fight I would dismantle him in seconds. Ronda would dismantle him in seconds – 100%. When you don’t know how to grapple you don’t stand a chance. For us, it’s like playing with a baby. People who don’t understand the sport cannot understand how vulnerable they are. There are always clinches and Ronda is a judo Olympian. She would throw Floyd on his head in a second. Me? I would knock him out. Cold.”

Mayweather might love money but he’s too smart to go down the MMA route. “Why would he take me on?” McGregor agrees. He pauses. “But if you’re talking about a fight that could generate half a billion – it’s this one. There’s never going to be another boxing fight like this. Only a cross-style match between Mayweather and me could generate that kind of interest and revenue. So maybe it could happen. I would certainly be up for it. I am capitalising on every single opportunity. It’s a strong word, one of my favourite words: capitalise. I’m ready to capitalise on everything.”