A new scoring system rewards difficulty, and Biles is taking advantage. Photograph by Pari Dukovic for The New Yorker

One night in April, at the Pacific Rim Championships, in Everett, Washington, the nineteen-year-old American gymnast Simone Biles approached the balance beam. A competitor from New Zealand had just finished her floor routine, set to the theme from “Game of Thrones,” and now Biles, who wore a pink leotard studded with more than four thousand Swarovski crystals, looked sternly down the length of the four-inch-wide balance beam, on which she was about to perform nine flips. “It comes down to this,” Al Trautwig, the NBC commentator, said.

That wasn’t strictly true. Biles was one of the last medal contenders to compete, but she was so far ahead in the competition that anything short of catastrophe would earn her gold. Since the world last paid attention to gymnastics, at the 2012 Olympics, Biles has become the first female gymnast to win three straight World Championships. If she wins three medals at this summer’s Olympics, in Rio de Janeiro, she will become the most decorated American gymnast of all time. “I feel absolutely terrible saying this,” Paul Ziert, the publisher of International Gymnast, said. “But if she doesn’t win five of the six Olympic gold medals it would be a disappointment.”

A low murmur began to build in the crowd as Biles revolved two and a half times on one foot, her other leg stretched parallel to the beam, then flipped while twisting a hundred and eighty degrees, all on a plank narrower than a standard American curb. The thrill of watching high-level gymnasts comes in part from the threat of disaster underlying the beauty of their routines—a strain that is often evident in the gymnasts’ faces. Biles, however, projects a sense of assured inevitability. “It’s like there’s no effort,” Steve Penny, the head of USA Gymnastics, said, seated next to me in the front row.

Gymnastics is one of the most popular televised events of the Olympics—some fans tune in for the acrobatics, and others for the tears—but its punishing physicality is better understood in person. When Biles executed a flawless back handspring, followed by a pair of backflips, it sounded as if the beam were about to crack in half. Penny convulsed ecstatically. “The beam is crying for help!” he yelled, throwing his hands into the air.

Two seats away, someone from the Canadian gymnastics federation shrugged and laughed in resigned defeat, which is more or less how the gymnastics world has reacted to Biles since she won her first World Championship, in 2013. “All the girls are like, ‘Simone’s just in her own league. Whoever gets second place, that’s the winner,’ ” Aly Raisman, who was the captain of the 2012 U.S. Olympic gymnastics team, and hopes to return for Rio, has said. Mary Lou Retton, the 1984 Olympic gold medallist, calls Biles the “most talented gymnast I’ve seen in my life.”

Biles paused at one end of the beam. “This dismount right here is the hardest dismount in the entire world,” Nastia Liukin, a two-time balance-beam world champion, said on the NBC broadcast. Biles launched into a pair of back handsprings that took her from one end of the beam to the other, at which point she leaped high enough into the air that as she flipped upside down twice, twisting a full revolution along the way, her dangling ponytail would have grazed the top of a basketball hoop. Biles stuck the landing as if she were magnetized to the floor, and Liukin declared her performance, in what is considered Biles’s third-best event, to be the “best routine ever.”

Biles stepped off the mat to a hug from Aimee Boorman, her coach, before striding over to Martha Karolyi, the brusque doyenne of American gymnastics, who has served as the national-team coördinator for the past fifteen years. Karolyi seemed to make a brief attempt at finding a teachable moment before simply pulling Biles into her chest. “That was spectacular,” Tim Daggett, the 1984 Olympic gold medallist and commentator, said. “The Russians, the Chinese—everybody is gonna be watching this, and they’re gonna be, like, ‘Give me a break.’ ”

Biles lives with her parents, Nellie and Ron, in a suburb north of Houston, ten minutes from the World Champions Centre, a fifty-two-thousand-square-foot gym that passersby sometimes mistake for a megachurch. After Biles won Worlds in 2013, Boorman told the Biles family that she wanted to leave her old gym; Nellie, who co-owned a chain of fourteen nursing homes around Texas, suggested that the Bileses build a gym. “My contribution was to say, ‘You should spell “center” differently,’ ” Ron, who is a retired air-traffic controller, told me. The Centre, which opened last November, is a gymnastics Valhalla, with a giant foam pit, forty-foot ceilings furnished with helicopter-sized fans, and a sign on the gym door advising parents that they are not welcome on the mat.

A few days after Pacific Rims, I met Simone there at nine in the morning, as she began a warmup that involved climbing twenty feet up a rope in five seconds, using only her arms. Biles is four feet eight, but she is all muscle, with jackhammers for legs and a tendency to bounce around a room, whether or not it has mats. The fact that gymnasts wear ribbons and jewel-flecked costumes—Karolyi has sent back leotards because she didn’t think they had enough crystals—can minimize how difficult the sport actually is. When Biles lands on each of her tumbling runs, she hits the ground with the force of two colliding football players, and she spends many nights after practice in a pair of pants that massage her legs with compressed air. She compares the process of getting into shape for competition as “repeatedly convincing yourself you aren’t going to die.”

The physical demands are just one obstacle in the way of a promising teen-age gymnast becoming an élite athlete. “She’s great eighty-five per cent of the time,” Boorman told me. “She is also fifteen per cent teen-age girl.” After her warmup, Biles, who doesn’t dispute the assessment (“I’m nineteen years old—I have emotional problems here and there”), burst into Boorman’s office at the W.C.C. to say that a boy she was not calling her boyfriend, but whom she would kill if he started dating anyone else, had just had his ears pierced. Biles, who is bubbly by default, attends church with her family most Sundays, and admits to enough of a shopping problem that she might need repenting: during a day off at Pacific Rims, she went to the outlets and bought a Kate Spade bag and a Michael Kors iPhone case.

Biles started homeschooling when she was thirteen, and graduated from high school last year, which means that she has been able to devote the past year to training for the Olympics, and to maintaining a hundred-and-forty-day streak of exchanging Snapchats with her non-boyfriend. Boorman said that when she first met the boy she told him, “I think you’re sweet, but if you screw with her mind I will kill you. You can screw with her mind after the Olympics, but not before. I’ve got enough to deal with.”

Biles was born in Columbus, Ohio, but at the age of two she and three siblings were taken from their mother, who struggled with drugs and alcohol, and placed in foster care. Ron, who is Simone’s grandfather, and his second wife, Nellie, agreed to take in the children. After an attempted reunion with her biological mother failed, Ron and Nellie adopted Simone and her younger sister, Adria, in 2003. (The other siblings moved in with Ron’s sister.) Simone considers Nellie and Ron her mother and father.