After Michael Phelps retired from swimming following the Olympic games in 2012, he was arrested for a second DUI in 2014 and entered a rehab facility in Arizona. Now, he is focused on training to make history and return to a fifth Olympics in Rio. (Jayne Orenstein/The Washington Post)

There will be new chapters of old books, for sure, because Michael Phelps is here for his fifth Olympics as a new father and a husband-to-be and Kerri Walsh Jennings will compete in her fifth Games with a new volleyball partner and another toddler, her third. Allyson Felix and Justin Gatlin on the track. Carmelo Anthony and Diana Taurasi on the court. Ryan Lochte. Aly Raisman. Gabby Douglas. We know these people. We know this Team USA, fully formed characters beamed back through our televisions every four years.

But here, too, comes Simone Biles , a fuse box struck by lightning who could prove so enthralling in the gymnastics competition that she draws eyes and hearts away from athletes across all sports. Here comes Trayvon Bromell, who became old enough to drink legally just last month but could push Gatlin and Jamaican megastar Usain Bolt in the glamour event that is the 100 meters. Here comes 20-year-old Kyle Snyder, who became an amateur wrestling legend during his time at Good Counsel and arrives in Brazil to go global with that reputation.

The American team that will walk in Friday night’s Opening Ceremonies at Maracaña Stadium will be led by Phelps, the most decorated Olympian of all time, whose latest honor will be carrying the stars and stripes ahead of his teammates. Behind him will be many of the members of a changed American team, 554 athletes strong, with 365 of them — nearly two-thirds — at the Olympics for the first time.

Visualizing the Rio Olympics in charts, graphics and maps

Among the regular Olympic characters in prominent sports who will be replaced here: Abby Wambach, the leading scorer in the history of women’s international soccer who won gold medals in 2004 and 2012 but is now retired. Natalie Coughlin, a 12-time medalist as a swimmer who tried to make this year’s team as a 33-year-old but failed. Sanya Richards-Ross, who last watched an Olympics in 2000, won’t be here to run the 400 meters again, her career complete with five medals. Misty May-Treanor, who teamed with Walsh Jennings to win three golds, retired after the last.

Even LeBron James, who first appeared in the Olympics as a teenager in 2004, won’t try for a third straight gold medal. In his place at a packed news conference here Thursday appeared a dozen American men’s basketball players. Only two — Anthony and Kevin Durant — were on the team that won gold in London four years ago.

So as America wakes up to the daily rhythm of the Olympics, it does so with a different team. And across all sports, that creates a different dynamic.

“You can see them. They’re so wide-eyed; their eyes are like this,” said diver David Boudia, who won a gold and a bronze in London, contorting his face while mimicking the seven first-time Olympians on the 10-member diving team. “We can help them with the experience, but they can provide some energy, too.”

Nearly a quarter of the U.S. team — 129 members — is made up of track and field athletes. Gatlin, 34, and Felix, 30, remain the stars. But during the trials process that concluded last month, new replaced old in a significant way. Eighty-six track and field athletes, a full two-thirds of the team, will be heading to their first Games. The average age of the group is less than 26, making this the youngest American track and field team since 1988.

So meet them, even in passing. Hurdler Sydney McLaughlin doesn’t turn 17 until Monday and can’t yet drive a car. Amy Acuff first represented the United States in the high jump in 1996, and she made four Olympic teams after that. This year, she will be replaced by Vashti Cunningham, the 18-year-old daughter of former NFL quarterback Randall Cunningham and a medal contender. Middle distance runner Clayton Murphy could challenge for a medal in the 800 meters, while Devon Allen, a wide receiver at the University of Oregon, could do so in the 110 hurdles. Both are just 21.

Gatlin’s head is graying, almost as if he can feel Bromell and 22-year-old Marvin Bracy charging up alongside him. Women’s sprinters Tori Bowie, 25, and English Gardner, 24, also could become household names, taking the place of medalists such as Carmelita Jeter.

“There’s a new era of sprinters that’s coming along,” Gatlin said during the trials, “and they got a lot of heart, got a lot of guts, got a lot of grit. When it’s time for me to leave, rest assured that I’ll be able to pass the torch on to Trayvon and Bracy and they’ll handle business.”

Swimming, too, experienced a transformation at its trials. The 47-member team features 31 first-timers. Phelps, with his 22 medals, 11-time medalist Lochte and defending Olympic champions Missy Franklin, Katie Ledecky and Nathan Adrian all have hopes of multiple medals here, and men’s Coach Bob Bowman called them “our tried and true guys.” But for the team to maximize its medal output, the new Olympians can’t just gawk at the surroundings, get chills from the environment and enjoy the ride.

“We’re going to be counting on [the veterans] to kind of fast-forward our younger swimmers so that it’s not an Olympics of an experience,” women’s Coach David Marsh said, “but it’s an Olympics of performance.”

That is true, regardless of sport. The United States has won more medals than any other country in four of the past five Summer Olympics, beaten only by host China in 2008. The goal here is the same. Phelps and Gatlin, Felix and Walsh Jennings — they’re all likely to contribute. But for another 100-medal haul, the opening pages of brand-new books must be written over the next two weeks, including characters we don’t yet know.

Rick Maese contributed to this report.