The Olympic Storylines You Absolutely Need To Know

With more than 300 events and 10,000 athletes at the Summer Olympics, you can't follow everything at the Rio Games even if you're an insomniac streaming NBC around the clock.

Still, you want to know which athletes, events and stories you can't miss. Well, it's impossible to say, because drama, heartbreak and triumphs can emerge anywhere, anytime at the Olympics.

But here are some of the best American storylines, packed with video links to give you a sampling of the feast that's in store:

Remember the name Ashton Eaton

For a defending Olympic decathlon champion heavily favored to repeat in Rio, Ashton Eaton is still relatively unknown outside the track world. That's starting to change now that he's prominently featured in promos leading up to the Summer Games.

If he wins again, you're likely to see him everywhere. Quiet and unassuming, Eaton has already set the world record twice. By definition, a decathlete is an all-arounder, a Jack of all trades, master of none. But Eaton is so talented, he could credibly compete in four individual events — the 100 and 400 meters, the 110-meter hurdles, as well as the long jump.

The U.S. has produced the world's greatest Olympic decathletes, from Jim Thorpe (1912) to Rafer Johnson (1960) to Bruce (now Caitlyn) Jenner (1976). Yet only one American ever won the decathlon twice, Bob Mathias, in 1948 and 1952. With a second Olympic win, combined with years of dominance in between, Eaton could stake a claim to being the best ever.

And he's also married to Brianne Theisen-Eaton, a Canadian who's among the favorites to medal in the women's heptathlon.

Gymnast Simone Biles expected to outshine Gabby Douglas

Gabby Douglas was one of the brightest stars at the 2012 London Games, winning the women's all-around gold at age 16. She's back on the U.S. team, but the spotlight will be on Biles, 19, indisputably the world's top female gymnast.

Biles has been the U.S. champion four years in a row and the world champion for the past three. Her routines are both spectacular and precise, and at 4-foot-8, she rockets off the tumbling mat as if it were a trampoline.

U.S. women now dominate the sport, and the five Americans in Rio are prohibitive favorites in the individual and team events. Yet this is a recent development. The U.S. women have only won team gold twice: the "Fierce Five" at the 2012 London Games and the "Magnificent Seven" in 1996.

Michael Phelps makes one last splash

He's the first American male swimmer to make five Olympic teams and likely to add to his Olympic record total of 22 medals, including 18 gold. He'll be competing in three individual races and possibly a relay.

Phelps said his heart wasn't into swimming in 2012 — rather stunning since he won four golds and two silvers — and his troubles out of the water have been well-documented.

"Going into 2012, it was like pulling teeth. It was brutal. You could barely get me to the pool," he said this spring.

But with retirement a certainty after these Games, Phelps says there was no slacking off this time around.

"I wanted to do it the way I should've done it in 2012," he said at the Olympic Trials. "I wanted to prepare for an Olympic Games like I should've."

Katie Ledecky may need an extra suitcase for her medals

Katie Ledecky introduced herself to the swimming world as the surprise winner of the 800 meters in London at age 15. The expectations are far grander in Rio.

She now holds 11 world records. She won five gold medals at the world championships last year. She won three individual races at the U.S. Olympic Trials and is also likely to compete in a relay at the Games.

Still a teenager, Ledecky could be just as dominant in the women's distance events as Phelps was in the sprints in his prime.

"I love being in the water," she told Sports Illustrated recently. "I love training. I hate when I have to take a week off. At the end of the season, I always take a week or 10 days off or longer, and I really don't like it. That's when we go to [the training pool] the most, and sometimes I have to do laps because I just get way too anxious."

Can Jamaica's Usain Bolt three-peat?

Usain Bolt was the clear favorite to win an unprecedented third 100-meter title in one of the glamour events, but he tweaked a hamstring in early July. While he appears to be recovering well, it's still not clear whether he'll have his top gear — a gear no one else has.

The result is a 100 meters that could be wildly unpredictable. Jamaica, arguably the biggest overachiever in the Summer Games, is again loaded with sprinters. The main challenge comes from the U.S., including Justin Gatlin, who has his own backstory.

Gatlin won gold at the 2004 Olympics, but he's twice been suspended for doping, once in 2001 and again in 2006. Yet he returned to the Olympics in 2012 and won the bronze at 100 meters.

At age 34, Gatlin is a senior citizen among sprinters, yet he reeled off a blazing 9.80 at the U.S. Trials, the world's fastest time this year. He also won the 200. Look for a wide-open Olympic final in the 100, packed with Americans and Jamaicans.

U.S. women rule team sports

The women's basketball team is so good, they rarely face close games in international competition. With the likes of Brittney Griner, Tamika Catchings and Diana Taurasi, all stars in the WNBA, the women are shooting for a sixth straight gold.

On the soccer field, the American women will be chasing their fourth consecutive gold, led by familiar names like goalkeeper Hope Solo, midfielder Carli Lloyd and forward Alex Morgan.

The women's water polo team and the women's eight in rowing are also reigning Olympic champs and are again favored. And we've already discussed the gymnastics team.

American women weren't always this dominant on the world stage. One big reason they are now is Title IX, which has upgraded women's sports nationwide.

Claressa Shields' Cinderella story: Round 2

Claressa Shields was one of the more inspiring stories at the London Games. A 17-year-old from a rough part of Flint, Mich., she fought her way to gold in the first Olympic boxing competition for women.

Shields returned to high school in Flint, where she lived with her coach because her family situation was so unstable. She slept with her gold medal wrapped around her wrist.

But in many ways her life didn't change much. The gold didn't make her rich or wildly famous. She receives a small stipend from the U.S. national boxing teams, which she uses to help pay her family's bills.

She's getting more attention in the run-up to Rio. She's featured in ESPN's Body Issue, wearing nothing but boxing gloves. And she's brimming with confidence this time around.

"In Rio, what's going to happen, everybody's going to be talking about that girl Claressa Shields can fight," she says.

Galen Rupp and Bernard Lagat try to revive U.S. distance running

U.S. men excel in the sprints and field events, but haven't been a real force for decades in distance races, where Kenyans, Ethiopians and other African runners usually fill the medal podium.

Galen Rupp won a surprising silver in London at the 10,000 meters, the first time an American man medaled in that event in nearly a half-century. In Rio, he'll run the marathon in addition to the 10,000 meters.

It's a grueling combo. So how does he prepare? He trains up to 140 miles a week. Do the math — that's 20 miles a day, not that far from a daily marathon. He bedecks his arms and legs with strips of black tape at the request of Nike researchers. It may not make him faster; it does make him stand out.

Meanwhile, Bernard Lagat is going to his fifth Olympics ... at age 41. He's the oldest runner ever to make the American team (though just by a few months. Meb Keflezighi, who turned 41 more recently, qualified in the marathon).

Lagat made the team by unleashing a ferocious kick in the final lap of the 5,000 meters to blow past the field, including Rupp, at the U.S. Olympic Trials. You need to see it to believe it, and you can below.

Russia's doping scandal

Russia's track and field team, which has 68 members and is among the best in the world, has been banned for systematic, widespread doping. The entire Russian Olympic team, which includes more than 300 additional athletes, narrowly escaped a collective ban.

Russia's doping program was part of an intensive, state-sponsored effort and is one of the most egregious ever uncovered, according to the World Anti-Doping Agency.

The Russian case means doping will once again be a major topic of conversation during the Games. Testing this year has found that an additional 98 athletes in the 2012 and 2008 Summer Games were using banned substances, including dozens of medal winners.

The question is whether Olympic authorities will start imposing harsher penalties, like the one applied collectively to the Russian track team.

Rio's travails

Brazil is the epicenter of the Zika virus. Violent crime is on the rise. The economy is in a major recession. And the president is being impeached.

The country has lurched from one crisis to the next as the Olympics approach. But Brazil does have a knack for spectacles. It pulls off Carnaval every year and was a worthy host of the 2014 World Cup in soccer.

In the run-up to the Games every four years, there's always a slew of stories about everything that could go wrong. And the list for the Rio Games is longer than most. But in the end, the Olympics tend to come off with only a few hiccups.

When the Games have been marred by tragedy, it's happened in places where it wasn't expected. The 1996 Olympics in Atlanta were humming along when an American set off a bomb, killing one woman and injuring dozens. And the 1972 Munich Games were proceeding apace when Palestinian terrorists struck, killing 11 Israeli athletes and coaches and one West German policeman.

Greg Myre is the editor of The Torch blog.