Maria Lucier, a retired paralegal from Frenchtown, Montana, was shaking her legs at Arthur Ashe Stadium, the nerves getting to her. Like so many in the U.S. Open crowd on the Friday, she had made a pilgrimage to see Serena Williams make history. Williams was going for a sweep of all four major tournaments of 2015, to clinch the first calendar year Grand Slam since 1988, and Lucien made her first ever trip to the Big Apple to see it happen. “She’s got cojones, you know?” says Lucier, explaining why she “idolizes” — her words — Serena Williams.

But so, it turns out, does an unseeded Italian player named Roberta Vinci, who was about to kill all of Serena’s Grand Slam dreams. “I thought she was going to spank her,” Lucier says. Turns out Vinci’s hands, too, were shaking down on the court; she too couldn’t believe it. Fans trekked in from all over — from Wisconsin, New Orleans, Houston, California, Montana — to see Serena remove any ounce of doubt that she’s the greatest female athlete of all time. They were black and white, women and men, boys and girls, who talked about how Serena inspired them on the tennis court, or to go to the gym when they don’t feel motivated — “I know Serena’s probably working out,” said one fan — or helped boost their own confidence.

She’ll still go down as the greatest. The coronation, however, will have to come later, as Vinci shocked Williams 2-6, 6-4, 6-4 in what was supposed to be a sleepy semifinals afternoon. “I think she played literally out of her mind,” Williams said afterward. Vinci didn’t dispute this, calling it the match of her life. But Williams didn’t help herself; she double faulted back to back in the third set, returned soft Vinci serves wide, and was unusually sluggish. Rather than smashing lobs, she lunged at them. “She was moving very slow, no movement in her lower body,” her coach, Patrick Mouratoglou said. “I think she lost her way mentally … Tactically, she didn’t know what to do at a certain point, and when you do the wrong choices, you lose the points you’re supposed to win.”

It was a stunning end to a summer when Williams at times seemed indomitable. At the French Open, Serena got so sick after the semifinals, she was curled up in a fetal position, shivering and crying in the locker room for at least 45 minutes. Her mother and older sister Isha had to undress Williams out of her drenched match clothes as she couldn’t do it herself. Isha made her sip Gatorade and fed her bits of a banana. “Just another bite, just another bite,” she said. She didn’t practice the next day, and Mouratoglou says Williams had a 104 degree temperature at 10:00 pm the night before. “You’re at this distance,” the coach, who was sitting five or so feet away, says, “and you feel the heat of her fever. You’re like, wow, how is she going to play tomorrow?” She beat the Czech Republic’s Lucie Safarova in straight sets.

“Strong is beautiful. And it’s powerful.”

At Wimbledon, a strange–though given modern-day racial and gender politics, unsurprising–brouhaha about her body exploded during her run to the championship. A conservative commentator openly wondered whether Williams was taking steroids, a New York Times story featured an opposing (male) coach and a few players taking veiled shots at her physique, and a few social media trolls called her manly. (Writer J.K. Rowling came to her defense with an epochal tweet: a picture of Williams in a sleek, sexy getup, with the words, “Yeah, my husband looks like this in a red dress. You’re an idiot.”) Such racially-charged remarks have long been part of the Williams sisters’ narrative: last year, for example, the head of the Russian Tennis Federation referred to Venus and Serena as “the Williams brothers.”

During an hour-long interview with TIME at her hotel in Toronto on August 9, where she was in town to play a U.S. Open tuneup tournament, Williams was eager to respond to the dialogue. “It’s important to touch on the body image issues,” Williams says. “I’m interested in doing the best than I can and winning grand slams and being a champion and, you know, everyone has different goals … I’m not out there thinking, OK, I’m not going to go to gymnastics class today because I don’t want to look fit. I literally was born with this most amazing body, and to be historic, and to amazing, and to be badass. And if anyone doesn’t like it, then they don’t have to. Because at the end of the day, I like it. And I know a lot of other people who like it too.”

She’s taken to social media to promote a positive body image. “I started hashtagging strong is beautiful all the time,” she says. “And people have to be in love with who they are, and it doesn’t matter what people say. Negative comments, you’re going to have those naysayers and those people who are unhappy and that kind of hide behind a computer. Or not hide at all. People are bold nowadays, who cares. But strong is beautiful. And it’s powerful. And you know, it’s been amazing for me. It can be amazing for anyone.”

Williams starts listing her favorite attributes. “Am I allowed to say my smile?” she asks. “Is that like a part? I always say my smile, because I think you can walk down the street and smile and make someone happy. But I also love my legs.” She stretches out her left one. “I love my waist too.” Wearing a casual black shirt and white jacket, she points, twice, to her chest. “I mean, hell, I love these ladies,” Williams says, cracking up. “Oh, and I love my ass,” she says, laughing louder.

At Wimbledon, Williams had just won her second Serena Slam — four straight major titles, though not in the same calendar year. “It’s about, oh, she’s muscular,” Williams says. “I just won a Serena Slam. How bout it’s just about that? And I just felt that’s kind of weird. And I was a little surprised. Like, really? And then I felt positive after all the support I got. I went to the gym after that, and I started doing more flips. I’m like, you know what, I’m going to make people get angry and get more fit.”

“What black guy, or woman, was killed this week?”

2015 was also the year Williams started to grow more of a social consciousness. In March she returned to Indian Wells tournament, site of one of the lowest moments of her career. In 2001, Williams was supposed to play her sister in the semifinal, but Venus backed out because of injury. Many in the crowd, convinced that Richard Williams, Venus and Serena’s father, conspired to prevent the sisters from playing one another, jeered Serena in the final. Serena felt a decidedly racist undercurrent. She vowed to never return.

But after reading Nelson Mandela’s autobiography, Long Walk To Freedom, Williams started to change her mind. The book moved her to tears. If Mandela forgave his jailers, how could she still hold such a grudge? Williams takes a deep breath. “I was brought up on forgiveness and love,” Williams says. “Have I shown that? I had to look in the mirror. Maybe I wasn’t treated fairly. That doesn’t matter at this point. But have I been able to let go?” Williams says going back Indian Wells may be the most important moment of her career.

As part of her return, she helped raise money for the Equal Justice Initiative, a non-profit dedicated to racial justice and fighting mass incarceration. The recent surge in law enforcement violence against unarmed blacks irks Williams, like it does for so many Americans, particularly African-Americans. In August, after Christian Taylor, a college football player in Texas, was shot and killed by a white police officer in training after an alleged altercation at an Arlington, Texas car dealership, Williams fired off a tweet to her, at the time, nearly 5 million followers: “Really??????!!!!!!!!!!? are we all sleeping and this is one gigantic bad nightmare? ‪#ChristianTaylor how many hashtags now?” It’s been retweeted more than 14,300 times, and is one of Williams’ most viral posts. “I just feel like, as black people, we have to stand up for each other. If I get slack for it, I’m okay with that now. You can hate if you want to. But this is now I feel,” Williams says. “It’s discouraging as a black person in America reading about yet another black person that’s been killed. Oh, what day of the week is it?” Williams looks at her watch. “It’s Monday? OK, so who got killed? What black guy, or woman, was killed this week?”

Williams sees herself taking a larger social role going forward. “I’m comfortable being a pioneer and a leader and an advocate,” Williams says. While she looks up to Muhammad Ali, she’s not going to make that comparison. “I’m still growing and I’m still learning and I would never be presumptuous and say that I’m in that position,” Williams says. “I don’t know if I can impact change. But I do know it’s better than me being quiet.”

“I just really, really honor the fact that she is doing her own thing, she’s her own woman, and she’s like, yeah, I’m going to talk about this,” says Alicia Garza, one of the founders of the Black Lives Matter movement. “I’m going to do the work necessary to make sure that we get closer to where we think we need to be. That is exactly what this moment is all about.”

“I’m not going to make any predictions”

Williams stretches out in a SUV while stuck in traffic on the outskirts of Toronto, on her way back to her hotel after an August 10 practice session. She touches on a few other topics between emails and bites of brown rice and salmon. She thinks a favorite media storyline – that Maria Sharapova, a “rival” that Williams has defeated 17 straight times, makes more endorsement money than her – is overblown. “The success of some other woman should be an inspiration to another female,” says Williams. “I don’t know why they make a big deal – she’s done amazing things, she’s gorgeous, who cares? I’m doing good for myself. I’m not struggling.” On if, given her power, she’s given enough credit for her all-around game and tactical ability: “I don’t think so. The thing is I hit really hard serves. People assume that’s what it’s about. It’s OK. I’m like that dark horse you don’t expect that’s happening. She just did that? I was expecting something else.” Is that annoying? “Yeah, I guess it could be if I sat and thank about it. But I try not to let too much bother me. I think if I did, I would be nuts. Totally nuts.”

So where does she see herself in five years? “I can’t answer that cause I definitely see myself five years ago playing tennis,” she says. “Now I’m just like, I’m not going to make any predictions. I could still be on the court. Oh God.”

Don’t expect her to hang up her racket in the immediate future. She’s going to try to break Steffi Graf’s mark of 22 Grand Slam tournament titles; Williams has 21. Margaret Court’s all-time record–24 majors–is within reach. Her diverse passions – fashion, philanthropy, acting – which were once seen as a distraction, have contributed to her longevity. Unlike so many tennis phenoms of the past, Williams didn’t burn out. As she ages, she appreciates and loves the game more and more.

After Friday’s particularly stinging loss at the U.S. Open, however, Williams cut all introspection short. “I don’t want to talk about how disappointing it is for me,” she said in her post-match press conference. “If you have any other questions, I’m open for that.” She darted out of the tennis center into a car. Gone from the Open, yes. But soon to be heard from again.

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Write to Sean Gregory at sean.gregory@time.com.