Three athletes caught the attention of millions a fortnight ago during the Opening Ceremony.
High-fiving, laughing and dancing under the Olympic flag, they marched under the banner of "Independent Olympic Athletes" - competitors without a nation. So how is that possible?
This weekend, marathon runner Guor Marial, from South Sudan, will make his Olympic debut. Marial, who escaped after being abducted by armed fighters as a child, fled the country as war broke out, and lives in Arizona, in the United States, but does not have a US passport.
Sudanese refugee Guor Marial will compete in the men's marathon as an independent
He lost 28 family members in the war, and believes he owes it to them not to compete under the Sudanese flag.
He refuses to join the Sudanese delegation, saying: "“It’s not right for me to do that. It’s not right for me to represent the country I refuged from.”
So Marial will run under the Olympic flag. If he wins a medal, the Olympic flag will be hoisted, and the Olympic anthem played. South Sudan does not have an Olympic team.
"Some things are more important than Olympic glory. If I ran for Sudan, I would be betraying my people. I would be dishonoring the two million people who died for our freedom," he told the Huffington Post.
"I want to bring honor to my country. People who just want glory, the spotlight of the Olympics, they don't care about other people.
"I'm fighting for independent status because I do care. When I run, I want people to see me and say, "'He is from South Sudan.'"
Philippine Van Aanholt, an independent Olympic athlete, parades during the opening ceremony
The other three athletes come not from a newborn state, but from one which has ceased to exist.
Judoka Reginald de Windt, Lee-Marvin Bonevacia, a long distance runner, and sailing competitor Philipine van Aanholt, come from Curacao, which was until 2010 was part of the Netherlands Antilles.
But the Antilles is no longer independent, it has become part of the Netherlands. The three athletes chose not to join the Dutch team, but to compete independently.
De Windt was knocked out in the first round and van Aanholt came 16th in her race.