In a small room, down a side street in Philadelphia, Bernard Hopkins sits so close that, knee to knee, nose to nose, I can feel the heat of his unblinking gaze. This is the familiar interview routine of the world’s most intriguing fighter. It almost feels important to match such a fierce and admirable champion stare for stare, nod for nod, because Hopkins stands on the brink of another dark and frightening challenge which he plans to turn into exhilaration.

On Saturday night in Atlantic City, just two months before he turns 50, Hopkins will face a deeply dangerous man who is 18 years younger than him. Sergey Kovalev is the WBO world champion, while Hopkins defends the IBF and WBA belts in this light-heavyweight unification title fight. Hopkins knows the unbeaten Russian hits so hard one of his former opponents, Roman Simakov, fell into a coma and died after they fought in December 2011. Kovalev is called The Krusher and 23 of his 25 victories have ended in knockouts.

Hopkins smiles at the reminder. He used to call himself The Executioner because he liked walking to the ring with his head covered in a hangman’s hood. But Hopkins has always been more of a defensive master than a lethal exterminator. And now, 26 years into an extraordinary career, it seems fitting he should celebrate his strange longevity by changing his nickname to The Alien.

He reaches over to grip my wrist. A wintry sun is shining in Philadelphia but Hopkins’ fingers are so cold it is tempting to believe he might come from another world. “Do you understand the brilliance of this move – from the Executioner to the Alien?” he asks. “I thought about it at three in the morning and knew it was perfect. I’m almost 50 years old and, against Kovalev, I have no fear. I have no doubt. I have already bent time to my will.”

When Hopkins made his professional debut in October 1988 Ronald Reagan was the president of the United States, the internet had yet to be invented and Mike Tyson was considered an unstoppable force as the undisputed and undefeated heavyweight champion of the world. Hopkins, who is 18 months older than Tyson, had just spent five years in prison.

“Jail time, no internet time,” Hopkins croons. “Imagine that? I’ve been doing this since before the internet was even a dream in some guy’s head. That’s how far back I go. Twenty-six years and counting all the presidents who have gone, all the champions who have fallen, all the ways the world has changed. But here I am. Still the same, like nothing else there has ever been. Alien to everyone else out there.”

Hopkins sounds ready to become an extra-terrestrial again. Yet, for a man who has always stoked the fire inside by remembering the murky ghosts of his past, Hopkins also sounds curiously personable and inclusive. “I have so many people in this movement I’ve created,” he says as one old-timer yakking away to another. “I call it the 40-and-up club. Even if they don’t like me people want me to win. Why? Because there’s always someone out there who is being challenged by this young intern. Some young guy wants to take their job, for less pay and less insurance. I play on that. So now I am pacing the streets and little old ladies come up to me. They start talking.”

The venerable champion slips into the high, sweet wail of a little old lady from downtown Philly: “Oh Bernard, I’m 65 years old – give me a hug.”

Hopkins hugs himself and then makes a serious point. “I’m not downplaying my age – because humankind is such that people run away from their age. Especially women. Guys pretend not to care but they do. Age is not a good thing to most human beings. But, being an alien, I embrace it. That’s why women tell me their age. The men just say: ‘Do this for us, Bernard.’ Who wants a young whipper-snapper taking your place? So I flipped it. I made it less about me as the Executioner and more about the 40-and-up club.

“Some people are saying: ‘Hell, this might not happen again. The Alien versus The Krusher? This could be a once in a lifetime thing. This is something I could tell my grandkids.’ We normally catch on late when people pass on. Then, after it’s all over, we say: ‘What a remarkable man.’ We want to give you the roses when you’re dead. That’s how human beings think. I try not to think like a human.”

Yet Hopkins is irreducibly human. He looks older than when we met in Philadelphia six years ago – just before, aged 43, he fought Joe Calzaghe in 2008. His achievement is greater now, 10 fights on, but it’s also possible to see the impact of a ferocious life in the ring.

Hopkins is still the slipperiest old boxer you could ever meet – with the sharpest patter in the business. “On November 8,” he promises, “you will see the Alien. But you’ll also see a surgeon at work. Precision, life-saving skills. You’ll see the art of jazz brought to life. You’ll see Miles Davis, Duke Ellington, Charlie Parker. Most of them were on dope. It was part of their game, their groove, their jazz. But I’m pure jazz. All groove, no dope. You’ll see ring generalship that is smooth but alert, accurate not reckless. After the fourth round this fight will be basically over. He usually knocks people out by then. But Kovalev will still have me in front of him – taking his heart, stealing his soul.”

The Krusher fights with an expressionless mask, as if showing no emotion is the best way to keep compassion in check. When they met to announce the fight did Hopkins penetrate Kovalev’s inscrutable stare? “No. But most Russians are like that. Most of them have nasty attitudes and are poker-faced. It’s in their culture. And let’s not forget that Kovalev did some military training. That’s part of his discipline. But I’m assuming he was told to avoid getting in a head to head because no one can compete with me in a talking competition.”

Kovalev brings a frightening force which Hopkins faces with cool, measured intent. “Yeah,” he says, “Kovalev bangs hard. He has a real punch. But, take that power away, what else has he got? He’s a better puncher than me. But he’s not a better boxer than me. He don’t have my knowledge and ring wisdom. Experience? Oh my God. Big moments of championship fights? I have ’em, multiple times. When you assess anything in life you look at someone’s resumé. I’m applying for a job. OK, here’s my résumé.”

Hopkins gestures to an invisible document which, judging by the space between his bony fingers, is 50 pages thick. He then narrows his fingers until they hold an imaginary few pages. “There’s his résumé. Now the fight ain’t fought on paper. But it gives you the inclination to say: ‘My God, Hopkins fought … damn … so many great fighters.’ You look at who Kovalev fought and, by records, it’s not fair. On paper it’s a mismatch. But this country loves violence. So they love punchers. This slick old fox is crazy enough to enjoy that challenge. All foxes are crazy because they take so many risks. But the fox always banks on his wit. They go on their fox instincts to sneak in there and get that hen before the owner comes out. That’s me.”

Hopkins, who is studied and cautious beneath the showman’s chatter, must consider the truth that Kovalev punches so hard he took another man’s life. “Oh yeah – but when I first heard he’d killed somebody I wanted to fight him even more. We’re in a blood sport, man. We’re on the wild side. Every time you step into that ring there is the risk of death. But I can’t lose sleep about it. Killing is no big deal, unfortunately, but I thank Allah I’m still here after 65 fights. I would rather take my chances in the ring with 19 Kovalevs than walk these streets alone at 11 o’clock at night.”

Hopkins uses his thumb to gesture at the street outside on an afternoon when downtown Philly seems more sleepy than sinister. He walks me over to a window in the deserted Joe Hand Boxing Gym on Third Street. “There is more chance of getting shot out there,” Hopkins says softly. “But when you fear Allah you fear no man. I fear Allah but I also put the work in. You cannot go into combat without putting the work in. If you have that calm, and you’ve done the work, it’s not hard.”

We retreat to his office as Hopkins keeps talking. “I never stared down the barrel of any gun in my life,” he says. “I’ve been blessed. But I’ve walked them jail blocks around hard men. So danger makes me run to the fire where others will run away. I’ve been taking risks my whole life. But I prepare myself by knowing the repercussions of everything I do. Before jail I never thought about the repercussions. I just went ‘Boom!’ and spent the next five years in jail. It was the best five years in terms of understanding life and death.”

Hopkins has shown me the knife scars which are a reminder he was stabbed three times before he went to Graterford prison aged 17. He was sentenced to 18 years for nine felonies and, on the inside, he saw prisoners being raped and humiliated. He was saved by boxing. Smokey Wilson, imprisoned for life on a murder rap, introduced him to the discipline of the ring.

When he was released in 1987, Hopkins looked into the sneering face of the Graterford warden who said he would soon see the young prisoner in his same old cell. “I ain’t never coming back,” Hopkins said.

As he prepares for “war”, Hopkins remembers that jailhouse warden. “We all need naysayers to bring the best out of us. For me the main one is that warden telling me I’ll be back inside. I’ve used that for 27 years. The reason I don’t give up and let them shovel dirt over me is that the warden would love that. And ain’t it strange how life turns out? Smokey Wilson is doing great. He got life in ’78 and he’s still locked up. But Smokey’s living his dream through me.”

Hopkins once told me, in a bizarre twist, his sister works at Graterford. “She still does,” he exclaims. “Charmaine is a captain there. How about that?”

His wife, two daughters and son must suffer as he gets ready to fight Kovalev? “They don’t give a damn. They see where the cheque’s at.”

Hopkins utters these words with a straight face but I know they fret about him and he eventually smiles again. “They do worry, yeah they do.”

So how does he convince his family it is worth the risk to keep fighting? “I charm them. My daughter is 15 and she would say how much longer you gonna fight? I’ll say: ‘Oh, just a little more.’ That was five years ago. In who knows how many years she’ll be married with kids and you and me will be doing another interview. Your hair ain’t gonna be grey then. It’s gonna be white – or yellow. Keep it real, man. I like it.”

Naazim Richardson, Hopkins’ long-time trainer, made a telling point this week. In the final press conference he said, of Hopkins, “He is not only the oldest boxing champion – he is the oldest champion in any sport. We can’t even reduce him to boxing any more. He’s no longer just ours.”

Hopkins will be back in Atlantic City on Saturday , risking his life, and his legacy as contemporary boxing’s most remarkable fighter. He stretches out his cold hand again in warning. “I don’t want to be on nobody’s pound-for-pound list. I want to be on a list of one. A list marked ‘Different: Alien.’ No human can really understand how, in a sport as brutal and taxing as boxing, a guy can do this at 49. Yeah, we know he’s like a hermit. We know he stays in his house, sticking to his discipline, he don’t mess around, he don’t drink, he’s never out of shape. He’s up at five, pounding those dark and lonely streets. But how does he really do it?’”

Hopkins lets his words hang in the air. And then, after a long pause, he taps me on the wrist one last time and speaks in a near whisper. “They will never truly understand me. How can they? I am alien to them.”