We may never know who the world’s biggest Roger Federer fan is. To find this fervently and perhaps frighteningly devoted individual, we would need to survey the 14 million people who have made Federer their friend on Facebook, the 5.2 million people who follow him on Twitter, the 350,000 registered users at his website, rogerfederer.com, and the millions more who, as his opponents sometimes quietly complain, make the Swiss Maestro feel as if he’s playing tennis at home when he’s thousands of miles away from it.

We might also need to investigate Brazil. After visiting the country for the first time, in 2012, Federer told the Swiss paper Tages Anzeiger, “I met more fans that collapsed in tears than elsewhere. It was amazing how many were shaking. I had to practically take them in my arms and say, ‘It’s OK, it’s OK.’”

Yet even among that globe-spanning cross section of humanity, Michele Drohan, a Massachusetts native and Manhattan resident who has never set foot in Switzerland nor spoken with Federer face to face, says she “automatically wins any contest in which someone tells me they’re a bigger Federer fan.” Her trump card, you ask? The “RF” logo she has tattooed on the inside of her left wrist.

“I got it the day Fed won the French Open in 2009,” she says, while admitting that a celebratory beverage or two may have played a role in the decision. “My friends and family actually think it’s great, or so they say. Of course, there are a few people who think it’s nuts.”

It was so devastating, and I thought, ‘Uh oh, I really like this guy.'

The tennis nut is not a new phenomenon, of course, but fans of today’s players have made the term seem more apt than ever. The sport’s current crop of likable, durable superstars—Federer, Rafael Nadal, Novak Djokovic, Ana Ivanovic, Serena Williams, Caroline Wozniacki and others—have inspired impassioned communities of followers on social media and given the game’s enthusiasts a new, collective, sometimes obsessive voice. Few, if any, sports are better suited to the Internet; in any given location, tennis fans may be sparse, but they can be found in virtually every country. And when it comes to the most famous player, Federer and his traditionalist appeal know no boundaries.

Just ask Colleen Taylor, who works in IT software in Dallas. Taylor has been a tennis fan since 1976, the year she turned on the Wimbledon final and caught a glimpse of Bjorn Borg and his long, blond hair flying across Centre Court. But her crush on Borg was just a warm-up for the deeper involvement with Federer, and his extended family of fans, that Taylor has developed over the last decade.

“I started to follow him when he won Wimbledon for the first time [in 2003],” Taylor says. “I thought, ‘This guy is different, the things he can do with a racquet, he’s a throwback.’ But it wasn’t until he lost to [Marat] Safin at the Australian Open in 2005 that I realized how much I cared. It was so devastating, and I thought, ‘Uh oh, I really like this guy.’”

Taylor knew the symptoms, and she knew where they would lead—to a lot more cleaning and a lot less eating.

“If Roger played an epic match every day,” she says, “I would be a size zero and my house would be immaculate. Watching on TV, I’m a wreck, and the commentary drives me crazy when he plays. I don’t know why, but I have to mute it. In the Wimbledon final [in 2014], I had to walk away completely.”

Taylor may have kept these facts mostly to herself, though, if she hadn’t discovered an online universe whose citizens knew exactly how she felt.

“It was nice to find a bunch of people who didn’t think I was crazy,” she says with a laugh.

Taylor’s virtual community soon became a real one, and she’s now something of a celebrity among the Federer faithful. She has met up with fellow Fed fanatics at ATP Masters 1000 tournaments in Indian Wells, Cincinnati and Miami, where she unveiled the first “shh!! quiet! genius at work” banners that can now be seen at virtually every Federer match, tucked into a (not-so-quiet) corner of the stadium.

Taylor has twice served as the “courier” for what’s known among Federer-ites as the “Red Envelope.” Since 2003, fans on his website have been sending in short good-luck messages before each tournament he plays. These are pasted into a red envelope with an official sticker and handed to Federer—who knows all about the tradition—by someone traveling to the event.

What’s the man behind the Maestro like? Not surprisingly, Taylor was a bit tongue-tied when she met him for the first time.

“But he made it easy,” she says, “because he looks at you and talks to you. He really does care what you think. He really has an inner light.”

What is it about Federer, a mild-mannered family man from Europe’s least colorful country, that inspires this kind of devotion? First, we might want to ask what makes being a tennis fan such a uniquely intense experience.

In an individual, international sport like tennis, who you root for is a matter of personal preference. With team sports, we tend to stay local and stick by our hometown.

Tennis fans are free to choose anyone from anywhere; national borders don’t matter to those of us who follow the game closely. Supporting a tennis player is often instinctive and difficult to explain, yet it expresses something about us.

In no other sport do we catch every grunt, sigh, smile, twitch, fist pump, eye-roll, lip curl, hair flick, look of fear and jump of joy the way we do when we watch tennis players on TV. Seeing them for hours at a time, close up, in our homes, we can feel as if they’ve become a member of the family. Federer’s fans have watched him grow up over the past 15 years, from a teenaged, pony-tailed metalhead who loved pro wrestling to a slickly-coiffed Rolex-and-champagne spokesman with four children.

For Drohan, being a Fed fan feels personal. She doesn’t mingle or commiserate with an online community, and even believes that Federer “takes the rap” at times for his followers, whose fanaticism has helped inflate his status to saint-like proportions and given him an unwarranted reputation for arrogance.

“I think some of that is transferred from his fans to him,” Drohan says. “I’ve always found his humility charming. He’s really pretty guileless.”

But Drohan echoes other Federer fans when she describes his appeal. While she loves the flair in his game, and she’s thankful that he “saved tennis from the [Lleyton] Hewitt era,” she’s more impressed with how he carries himself as a person.

“He represents the game well,” she says. “He plays fair, he doesn’t look up to his box and he connects well with his fans. I guess I’m proud of the way he conducts himself. He embodies what I think an athlete should be.”

A similar phrase comes up often when you talk to other Federer fans: “He plays the game the way it was meant to be played.” Where he was once a throwback, Federer, with his one-handed backhand and net-rushing style, now looks like the sport’s one remaining connection to how it was played in the last century. Federer has always been a crowd favorite—during the Open era, only Borg has been as universally popular—but the audiences have become bigger and more vocally partisan as he has reached his 30s and begun to succumb to the vulnerabilities of age. He’s still the great one, but now he’s a little like us, too.

Among the Grand Slam nations, the theme that unites Federer fans is his sense of tradition—one that’s versatile enough that each country can see him as part of its own history. In Australia, they love him for the respect that he shows for their tennis legends.

“Roger is revered here,” says Courtney Walsh, a sportswriter for The Australian, “and I think the main aspect is the respect he has for the game and Australia’s part in it. As a colleague of mine said, ‘When Federer broke down in front of Rod Laver a few years back, it was as if he had become one of us.’”

In England, “he fits the image Wimbledon has of itself,” says one London tennis fan. The tournament sees itself as tennis in its highest and purest form, and Federer also personifies that. “I always remember Sue Barker [of the BBC] saying joyfully, ‘Has there ever been a more elegant champion?’”

In Paris, through his words and his artist’s touch on court, Federer shows that he’s fluent in the languages of the French.

“Roger, yes, he’s a god in France,” says Carole Bouchard, former writer for the French sports daily L'Equipe. “His elegance speaks to classic tennis fans. We cut off our king’s head, but we’re still deeply attached to traditions.”

At Roland Garros in 2012, Federer screamed at his Parisian faithful to “Shut up!” and stop distracting him. But they went right on paying tribute to their god.

The latter incident points to the way Federer’s elegant image has become a given at this stage in his career. He’s been presented that way for so long that any discordant notes he might strike are washed away with his next display of shot-making brilliance.

He embodies what I think an athlete should be 

That presentation isn’t a phony one. There’s a reason that his fellow players have made Federer the president of the ATP Player Council, and given him the tour’s sportsmanship award 10 times. But his strengths have also been judiciously marketed, first by IMG and now through his own agency. At the 2007 US Open, “Darth Federer” was born when Nike created black tuxedo shorts for him to wear during night matches.

“I thought it really looks cool,” said Federer of his attire. “In New York you can do such a thing. Nowhere else in the world.”

He has worn a white evening jacket on Centre Court. He’s sponsored by Rolex, Moët & Chandon, Credit Suisse, Mercedes-Benz and Lindt. He travels the world with an entourage that can resemble a small army. If Borg was the right player for the rock-star age, Federer is the right player for our new Gilded Age.

How does Federer feel about being the object of all of this devotion? According to him, his life requires some compartmentalizing.

“I have to constantly remind myself again about where I come from,” he told Tages Anzeiger in 2012, “and tell myself who I am. I also like the normal life—back to reality, family, friends; just quiet, please. And then sometimes I dip into the other incredible life I have.”

Federer’s most dedicated fans often see a less branded and more down-to-earth version of the man in their interactions with him. Like the Queen, Federer sends his fans a Christmas message on his website, thanking them for their support. He says their passion continues to motivate him, especially at smaller events. Near the end of 2013, one of his most frustrating seasons, when early-round losses and a back injury had many speculating that he might retire, Federer said he was inspired by the energy of the Chinese fans who came to see him practice in Shanghai.

“I expected some people to be there,” Federer said at the time, “but not hanging over the fence and holding up a banner [that says], ‘I believe in you.’ It gives me unbelievable motivation, inspires me to train hard, work hard, push further.”

For Colleen Taylor, it was hard to see Federer relinquish the grip he had on the game when he was at his best, and hard to see him begin the long, inevitable decline every champion faces.

“I went through a period of mourning,” she says. “But now I feel like I was lucky to be around for his prime, and I’m OK with whatever happens. I’ll enjoy what’s left, because there won’t be anyone like him for a long time.”