Tokyo 2020 will be the first time since 2008 that the decathlon gold medal is not awarded to the USA's Ashton Eaton.

The 33-year-old retired decathlete first earned Olympic gold at London 2012 where he defeated fellow US representative Trey Hardee by 8,869 points to 8,671.

Eaton, who hails from Portland, Oregon, then successfully defended his crown at Rio 2016. His score of 8,893 equal led the Olympic record and saw him defeat second-placed Kevin Mayer.

The double-gold winning champion hung up his cleats in 2017. 

Not content with dominating a red track, Eaton wants to follow in Neil Armstrong's footsteps and became the first person to set foot on another celestial body. In his sights is the red planet itself, Mars.

"I like things that are really ambitious goals and being first person on Mars would be a good one."

 "If in the future, things kind of come around and there's an opportunity, I'll take it," Eaton told the Associated Press.

"We saw Mars, clear as day. It was funny to imagine being there. Brianne [his partner] was like, 'Why go there? The earth would be a little green star in the sky.' I was like: 'Yeah, wouldn't that be incredible?'" he continued.

Having earned silver at the 2004 Olympics, Bryan Clay went one better in 2008 and earned the only Olympic gold of his career.

Clay's victory was monumental as he became the first American to win decathlon gold since 1996 and his winning margin of 240 points was the largest since 1972. 

The Texan won four of 10 events including the 100 meters, long jump, shot put and the discus throw. 

Just like Ashton Eaton, Clay clearly has an interest in everything upwards as he recently flew with the Thunderbirds, a US air demonstration team.

On the ground, Clay gives motivational speeches and runs his own fitness company.

The man who pipped Clay to gold in 2004 was Czech Roman Šebrle. Considered to be one of the greatest decathletes of all time, Šebrle's Olympic gold medal came in Athens when he sat a then-Olympic record of 8,893 points.

The Czech only won two of the ten events — the shot put and javelin throw — but scored highly in all the overs, helping to narrowly defeat Clay who scored 8,820 points.

In a similar style to Clay, Šebrle won gold having earned silver in the previous Olympics. In 2001, he became the first man to score over 9,000 points in a decathlon.

Since retiring from athletics, Sebrle has picked up his golf clubs and gone pro.

Ranked 1,889th in the world, Sebrle has played 17 pro events, but has never made the cut.

When he's not on the links, Sebrle works as a news anchor at Czech Television Prima.

Speaking to the Huffington Post in 2017, Serble said: "When I was down, it was difficult to cope with my situation, but then I decided to retire from the decathlon. It was not an easy decision. I had done decathlons for a very long time, even until I was thirty-eight years old.

"Then, producers from Czech Television Prima asked me to join their news team. I seized the opportunity. It was a very interesting offer, and I had never done it before, so I gave it a try.

"Working in television broadcasting is so different from athletics. In the first six months, it was very difficult for me to adjust to the new job, and I've worked hard to accumulate experience and acquire skills. I hope to improve better day by day."

The turn of the millennium saw the remarkable story of Estonian Erki Nool.

Growing up with the backdrop of a crumbling Soviet Union, it was not until he was 13 and his father sent him to a sports-focused boarding school that Nool started having three meals a day.

When Estonia gained independence in 1991, Nool declared his desire to be a part of the Olympic team and competed at Barcelona 1992, but had to pull out during the games.

Eight years later, he had developed into one of the world's top decathletes and, despite not winning a single event, he took gold at Sydney 2000, becoming a national hero in the process.

After retirement, Nool took the path from sportsman to politician.

He was elected to the Estonian Parliament in 2007,but has since left politics.

These days, he runs his own real estate business, but has not quit the world of sport entirely as he has his own athletics school. 

The last Olympic decathlon of the 20th century was won by the USA's Dan O'Brien who comfortably beat German Frank Busemann to secure gold in his home country.

At the beginning of 1992, the Portland-born athlete was the favourite to earn decathlon gold at that summer's games but during the US Olympic Trials, he failed to clear the bar on all three of his pole vault attempts. He slipped from first to finish 11th in the trials and did not qualify for the team.

O'Brien made amends in 1996 when, having won three World Championship golds between 1991 and 1995, he earned gold in Atlanta.

O'Brien has spent retired life in Scottsdale, Arizona with his wife Leilani. 

To keep him busy, the gold medal winner volunteers as assistant coach at Arizona State University and he helps to train athletes in sports such as tennis and football.

He has also co-written a book called "Clearing Hurdles: The Quest to Be The World's Greatest Athlete," which was released in 2012.

With O'Brien absent, the Czech Robert Změlík won gold at Barcelona 1992 in what was to be his last time representing Czechoslovakia before it became the Czech Republic.

The decathlon was held at the Estadi Olímpic de Montjuïc in the hills of the Catalonia capital and Změlík won two events, the long jump and 110m hurdles.

Změlík's victory came at the disappointment of the local fans as the Czech beat Spaniard Antonio Peñalver to the top prize.

Since retiring, Změlík runs his own business and after six years of experience, he set up his own dietary supplements company.

The business, called STARLIFE, operates in the Czech Republic, Poland, Slovakia, Romania, Hungary and India.

Representing East Germany, Christian Schenk triumphed at Seoul 1988, beating his compatriot Torsten Voss to gold.

Schenk scored highly in all 10 events but only won the high jump with a score of 2.27 metres.

He scored 8,488 points, narrowly beating Voss by 89 points to earn gold.

Schenk retired in 1994 but his Olympic medal came under threat 24 years later.

In August 2018, the German admitted to using the steroid chlorodehydromethyltestosterone during his career, but under the IOC statue of limitations, he was allowed to keep his medals. 

"We welcome the admission and hope that it helps to clarify the situation and strengthens the fight against doping." an IOC spokesperson said. 

Before Eaton, the last man to win back-to-back Olympic decathlon golds was Great Britain's Daley Thompson.

Alongside Eaton and fellow American Bob Mathias, Thompson is one of three decathletes to have two Olympic golds for the event.

His first success came at Moscow 1980 where he defeated the Soviet Union pair Yurif Kutsenko and Sergey Zhelanov with 8,495 points to their 8,331 and 8,135 respectively.

Following that, Thompson headed to Los Angeles where he would face his longtime rival Jürgen Hingsen. Between the two of them, they won half of the events with Thompson coming top in three and Hingsen in two.

Despite the fierce rivalry that had grown throughout the 1980s, Thompson had the last laugh as he beat Hingsen by 125 points to earn his second Olympic gold.

A persistent hamstring injury saw Thompson retire from athletics in 1992 but not from all sport.

In his retirement, he has played soccer for Mansfield Town reserves, Stevenage and Ilkeston, entered the 1994 Ford Credit Fiesta Challenge Championship, and become fitness coach for Reading Football Club.

He was asked to be an ambassador for the London 2012 Summer Olympics and opened his own gym in 2015.

Jenner — known at the time by her birth name, Bruce — beat the world record on the way to decathlon gold at Montreal 1976.

During the events, Jenner set personal bests in all five events of the first day, but still trailed Guido Krastchmer of West Germany. On the second day, Jenner took the lead after another personal best, this time in the pole vault.

The American never left the top spot and ended the final event of the decathlon, the 1,500 metres, on 8,618. A world record that stood for four years until Thompson bested the total. 

After the medal success, Jenner retired from the sport. 

Of all the past nine decathlon winners, Jenner has certainly had the most prominent post-retirement career.

Jenner began making TV appearances in the 1970s, before marrying second wife Kris Kardashian in 1991.

They, along with their children, stared in the reality show "Keeping Up with the Kardashians" which became a global hit and propelled the family to the heights of fame.

In 2015, Jenner came out as a trans woman and appeared on the cover of Vanity Fair with the headline "Call me Caitlyn."

In 2017, she completed sex reassignment surgery. 

Her latest venture sees her running for governor of California.