It's hardly a surprise -- Olympians are among the most driven, competitive people on the planet. So 2016 is no exception, with some monumental spats boiling over in the pool, on the track -- and even in the stands.
Here's a look at some of the great feuds that could come to define the Rio Olympic Games.
For more than a decade, the great American swimmer had vanquished all comers in the 200 meters butterfly on both the world and Olympic stage, but then along came Chad le Clos
The South African chased down Phelps -- his childhood hero -- in the final 50 meters of their meeting in London in 2012, to snatch a dramatic fingertip victory.
But, after retaking the 200-meter butterfly crown
, arms aloft and waving his finger, Michael Phelps left nobody in doubt just who was No. 1 Tuesday.
Previously, cameras had caught the American -- the greatest Olympian ever -- looking less than pleased as he sat patiently waiting in the "ready room" for the 200-meter butterfly semifinal. In front of him, le Clos is seen doing what can best be described as a shadow boxing-style dance routine.
But Le Clos shouldn't take it personally -- ultra-competitive Phelps also has a beef with USA teammate Ryan Lochte, with whom he resumed his rivalry in the 200-meter medley.
Mack Horton and Sun Yang
Australian swimmer Mack Horton narrowly beat China's Sun Yang in the 400-meter freestyle event -- but the deepest cut came out of the pool, when he accused Yang of being a "drug cheat
Horton sparked outrage across China -- a nation not always known to handle slights well -- for describing his narrow win as one "for the good guys." Prior to the race, Horton said Sun, who served a three-month ban for testing positive for a banned substance in 2014, was a "drug cheat."
Horton's Facebook, Twitter and Instagram posts were flooded with comments attacking him and demanding he apologize to Sun.
"You are too complacent and will die quickly," read a comment on one of Horton's Instagram posts. Others called him a "loser" and "shameful," and flooded the comments with a snake emoji. Chinese state media also joined in the outrage
The spat adds another dimension to the men's 1500-meter freestyle race on Friday, when Sun and Horton will face off again. Sun won gold in the 200-meter freestyle on Monday.
Lilly King and Yulia Efimova
In one of the most anticipated swimming races of the Rio Olympics, US star Lilly King backed up her fighting talk by defeating Yulia Efimova
to win gold in the 100-meter breaststroke. The Russian -- who had previously been suspended for testing positive for banned substances -- had drawn the ire of her rival by waving her finger in a "#1" gesture after winning her semifinal.
The Indiana native chastised the Russian ahead of the race, telling a reporter
, "You're shaking your finger No. 1, and you've been caught for drug cheating. I'm just not a fan. I'm going to go swim my heart out for USA and hopefully that turns out the best."
The American let her swimming do the talking. After bagging the gold -- by just under a second -- she told NBC reporter Michelle Tafoia that she felt she had made a statement on behalf of her country and other "clean" athletes.
"I hope I (made a statement) -- that we can still compete clean and do well at the Olympic Games and that's how it should be."
Justin Gatlin and Usain Bolt
Even the fastest man on the planet has some competition -- and it comes in the form of American Justin Gatlin, who will be looking to spoil Bolt's samba party in Rio this summer.
But the Jamaican insists he's unfazed by the man who won gold in the 100m in Athens twelve years ago.
"I don't think about him really," Bolt told CNN's Amanda Davies. "I always try to run the race in my head and try to execute. I definitely try not to sit around and think about people. I am trying to focus on working hard, executing and figuring out what I need to do to get it right."
But he did say that Gatlin would "feel his full wrath."
Gatlin responded amiably, saying that he just had to do what he "had to do." He said that he "hadn't really thought about" the possibility that the running track in Rio could be the last time the two greats meet.
Argentina and Brazil's supporters
Fans are getting in on the rivalries too. Brazil and Argentina will hold talks Wednesday to discuss the relationship between fans from both countries attending the Rio Olympics, according to a press release from the Brazilian government.
The meeting will take place in Rio de Janeiro, with the goal of encouraging "peaceful interactions" between Brazilians and Argentines during the Olympic Games.
Russian athletes have also been booed at the Games, with sports fans jeering during Friday's Opening Ceremony, turning the normally jubilant parade of nations into mixed commentary on the decision to let 271 of Russia's 389 athletes compete
despite a report accusing
the country of "state-sponsored doping."
But sport's greatest show isn't always driven by intense rivalry. A couple of gymnasts at Rio 2016 have taken to heart one of the founding principles of Olympism -- "placing sport at the service of the harmonious development of humankind" -- in a very modern way.
Gymnasts Lee Eun-ju of South Korea and Hong Un-Jong of North Korea posed for a charming selfie
, an impromptu photograph that's a rare occurrence by members of the two Koreas -- two countries which are still technically at war.