Pugnacious as he is on the court, Rafael Nadal, who's gunning for a fourth straight Grand Slam title at the Australian Open, is just as mild off it

Rafael Nadal does not tweet. He has no line of supermodel girlfriends, no lines on Entourage. He has no celebrity chef. He has no McMansion on the 18th green, no Manhattan crash pad, no tax-sheltered residence in Monte Carlo. A private jet? Please. Last summer Chris Fowler, the ESPN announcer, broadcast the Cincinnati ATP tournament and flew back to New York City in first class. As he gathered his suitcases at LaGuardia, he spotted Nadal. "Hey, Rafa, I didn't realize you were on the flight," Fowler said. Then he realized that Nadal had been sitting in the back of the plane.

This was no fluke. Fresh from winning the Tokyo ATP event last October—and surpassing $9 million in prize money for 2010—Nadal surprised other passengers on Air China's 3½-hour flight to Shanghai by settling into seat 29C. "I listen to my music," Nadal says of his in-flight habits. "It sounds the same as it does in [first class]."

In men's tennis, though, Nadal occupies seat 1A. If 2010 marked the year that Spain became a sports powerhouse—a World Cup title for the national soccer team, a Tour de France victory for Alberto Contador and another NBA ring for the Lakers' Pau Gasol—Nadal was el mejor de todos. He not only took the top ATP ranking from Roger Federer (who travels on NetJets) but also won three of the four major singles titles. When the Australian Open begins in Melbourne on Monday, he will try to do what no other man has achieved since Rod Laver in 1969: earn a fourth straight Grand Slam championship.

Barely a year ago Tennis Nation came to a rare agreement and declared Federer the best player in history. Now it's reconsidering. Nadal has won nine majors to Federer's record 16, but at age 24 he's ahead of Federer's pace. Plus, Nadal leads their head-to-head series 14--8. All of that makes for a heated debate, but don't expect Nadal to fan the flames. It's not just that he declines to toot his own vuvuzela—he casts his vote for the other guy. "For me, it is Roger," Nadal says. "What he does for so many years is incredible."

Great as their on-court rivalry may be, there's so little tension between them that this off-season they played three exhibition matches—including one in Switzerland to benefit Federer's charity and one in Spain to benefit Nadal's. (Nadal won two of the three.) A commercial to promote the home-and-home series took unnecessarily long to tape because Federer and Nadal kept making each other laugh. Ali-Frazier this isn't.

Like Federer's courtliness, Nadal's almost pathological humility serves him well when he plays. How can an opponent summon the animus to beat a guy who is so damn nice? Anyone can make a self-effacing remark at a press conference; Nadal has done it so often that it's beyond calculation. As Nadal paraded around Arthur Ashe Stadium with the U.S. Open trophy last September after beating Novak Djokovic in the final, he spotted his vanquished foe leaving the court. Nadal immediately stopped, put down the trophy and clapped, letting Djokovic soak up the applause. "Rafa was raised by a good family," says the Spanish player Fernando Verdasco. "Good values."

The lone knocks on Nadal are that he indulges in a bit of psychological warfare—before the prematch coin toss to determine who will serve, he makes his opponent wait at the net while he sits courtside, sips water and eats an energy bar—and that he has received mid-match guidance from his uncle and coach, Toni Nadal. The latter transgression, a breach of ATP rules, ignited a firestorm on tennis message boards. Yet in 2010 fellow players voted to give Rafa the Stefan Edberg Sportsmanship Award. "That's such a satisfaction," Nadal says. "The players know who is fair and who isn't."

Imposing results, exceeding popularity and looks that aren't exactly troll-like—sounds like marketing gold, doesn't it? Yet while Nadal is indisputably a global star, his endorsement portfolio is estimated at $17 million, less than one third of Federer's. In the U.S., in particular, he remains underexposed. Some of this is due to his English, which is still endearingly flawed (doubts, to Nadal, are dubits) leaving him unprepared for, say, Jon Stewart's guest chair. But perhaps more important, Nadal has no use for the trappings of fame. Award-show appearances and celebrity "brand extensions" just aren't part of his M.O. (For this story, his camp consented to an interview but declined a photo shoot.)

When Nadal's handlers attempt to "fame him up," bad things happen. Last year he appeared as an awkward bystander in a Shakira video; now it's among his least favorite conversation topics. His agents landed him a deal with Richard Mille, a watchmaker whose timepieces sell for as much as $500,000. Sure enough, Nadal lost the watch.

So, Rafa, when are you finally going to start acting like a star?

"You mean have bodyguards?" he asks.

No. But, sure, what were you going to say about that?

"When you have bodyguards, everything is more difficult. That's when people recognize you. When you go normal, it's easier to go out without problems, people are respectful. O.K., maybe you sign autographs or do photos, but no problem."

But beyond bodyguards—

"I have to be myself. I cannot be someone I am not."

Roger Federer is such a graceful tennis stylist that Nadal has been cast in the role of the grinder, Hephaestus to Federer's Apollo. The contrast is entirely too facile. There's artistry in Nadal's capacity to go from defense to offense in a single stroke, and in his ability to generate ungodly spin on shots whose angles defy the laws of geometry. "The nuances aren't past him," says Andy Roddick. John McEnroe calls Nadal the most skilled net player this side of Federer.

But if Nadal isn't a natural, he's used that to his advantage. "It's given me motivation to keep working on improving," he says. Has another champion—in any sport—made such radical upgrades from year to year, forever expanding the borders of his ability? In this, perhaps, Nadal resembles the athlete to whom Federer is so often compared: Tiger Woods. A few years ago, determined not to be another Spanish clay-court specialist, Nadal worked on his grass-court skills, shortening his strokes and hugging the baseline. He hasn't lost at Wimbledon since 2007.

Last year Nadal went to New York City hell-bent on ending his string of defeats at the U.S. Open, the one major he had never won. "I know I needed to serve better," he said. Adjusting his grip and sacrificing spin for power, he added 10 mph to his serve. Nadal dropped just one set in seven matches, completing the career Grand Slam at 23.

"People think once you are a pro, you're done improving, it's just tournaments," Nadal says. "That cannot be. Sometimes it might be a [stroke], sometimes it might be attitude, but you can always get better." The thought hangs; then he adds, "Other players might feel different."

Late one afternoon in London in November, Nadal practiced with Marc López, his sometime doubles partner, flown in for the week to serve as his sparring partner. This was a playful session, two countrymen rifling shots and trash talk at each other. If you didn't know the identity of the players, you might not have guessed that López is ranked 723 spots lower. He hung in during the rallies and served as hard as Nadal. So why the disparity in their careers? "The problem," explains another Spanish player, "is that Marc s---- his pants when there's pressure."

This underscores what might be Nadal's ultimate talent. Perhaps no other athlete—never mind tennis player—is psychologically so tough. When Nadal competes, he seems blind to the very concept of failure. He's made a career out of meeting the moment: Of the 11 Grand Slam finals he has reached, Nadal has won nine. And the two he lost were at Wimbledon in 2006 and '07, against Federer in his absolute prime. "People look at Nadal, see the muscles and say, 'He's a beast,' " says doubles specialist Mike Bryan of the U.S. "No, mentally he's a beast."

How does someone with no taste for conflict in every other dimension of life—asked when he was last in a fight, Nadal says, "Oh, never. Never. I get very scared"—become such a warrior on the court? Nadal grew up comfortably in Manacor, Majorca, in a large, supportive family, so he's not channeling some childhood struggle. He plays with no anger, so he hasn't manufactured a conflict in his mind. Asked whether he's worked with a sports psychologist, he laughs and repeats the question in Spanish for friends. "I don't believe [in that]," he says. "Maybe for big problems in life. But for sports? If you need that, you're not ready to be here!"

Pressed for insights, Nadal has two. Starting when he was a kid, his uncle made him go without water during long stretches of practice and spend extra time on the court when the weather was hottest. "It's difficult to practice the pressure of a fifth set of a Grand Slam, but if you practice your whole life with high intensity, staying there mentally when the big moments arrive is less difficult," Rafa says. Second, he says, "I am very positive. I am normally happy, and that helps. You don't have to be mad to have intensity." He scrunches his face, unhappy with his answer. Then he reloads: "I love being Number 1, but I loved being Number 2 too. It doesn't make a big difference. What makes a big difference is when you go on court and be competitive."

After his hitting session with López, Nadal retreats to his dressing room in London's O2 Arena, stopping, of course, to sign autographs and appease the smartphone paparazzi. Pugnacious on the court, he is solicitous with fans and tournament staffers. A day earlier when Nadal had folded his 6' 1" frame into the backseat of his courtesy car, the driver had asked, "Do you have a enough room?"

"Fine, fine," Nadal replied. "Do you have enough room?"

Now Nadal is followed out of the arena by his support team. There's Uncle Toni, who draws no salary from Rafa but instead has a share of the Nadal family construction business in exchange for his services. There's Benito Pérez-Barbadillo, a former ATP staffer who serves as Rafa's public relations manager. There's Rafael Maymo, a physiotherapist from Majorca who keeps Nadal fit and limber, doing his best to stave off injuries, especially to the player's tendinitis-prone knees. "We're like a traveling family," says Pérez-Barbadillo. "We have little fights, but Rafa doesn't fight so much."

Nadal and his team head out the back of the arena and board a motorboat down the Thames to their hotel. They'll change, then go to a sports bar to watch soccer. As the engine guns, the men whip out the iPads their boss gave them last fall. Rafa, though, looks out the side of the boat. He wears a ski coat and a scarf above the waist, shorts and Nikes below; try as he might, he can't conceal his essential jockiness.

Seeing that the dignitary on his boat is taking in the scenery, the captain points out the sights: There's Big Ben. We're coming up on London Bridge. By the time they're done with construction, this building, the Shard of Glass, will be the second-tallest skyscraper in Europe.

The captain motions to a domed building on a hill. It's the Royal Observatory, where Greenwich Mean Time originates. "That," he says, "is where every new day starts." Tennis's man of the present ponders this, smiles and says, "Does this mean we're in the future?"

Now on SI.com

Follow the Australian Open and read Jon Wertheim's Tennis Mailbag at SI.com/tennis

"I LOVE BEING NUMBER 1," NADAL SAYS, "BUT I LOVED BEING NUMBER 2 TOO. IT DOESN'T MAKE A BIG DIFFERENCE."

PHOTO

Photograph by MIKE POWELL

FIST-PUMPED UP Nadal exulted last July after winning his second Wimbledon singles title and cementing his place atop the men's game.

PHOTO

STEFAN WERMUTH/REUTERS

TRADING PACES Nadal used a power serve to win the U.S. Open, but after matches he can throttle back with Federer and fans.

PHOTO

SIMON BRUTY

[See caption above]

PHOTO

IMAGO/ZUMAPRESS.COM

[See caption above]