Marathoner endured refugee camps, fled forced servitude in order to realize his Olympic dream

South Sudanese Olympian Guor Marial may not be a medal threat in Sunday's marathon, but the former slave's road to Rio is one of the most astonishing stories of these Games.

As a teenager Marial was forced to run for his life during Sudan's long civil war, in which he lost 28 members of his family, was kidnapped twice and ended up in forced servitude.

When he fled Sudan he never wanted to run again because of the traumatic memories, but after arriving in the United States as a refugee his talent was quickly spotted by his teachers.

This month Marial made history when he became the flagbearer for South Sudan's first Olympic team, leading compatriots Margret Hassan and Santino Kenyi into Rio's Maracana stadium during the opening ceremony.

This is Marial's second Olympics, but the first in which he can wear his national colors.

Four years ago in London he had to compete as an independent under the Olympic flag because South Sudan - which only gained independence the year before - was unable to send a team.

Marial told the Thomson Reuters Foundation at the time how he dreamed one day of representing his homeland. "I will be wearing the Olympic uniform, but inside I will be holding the South Sudan flag in my heart," he said.

In a recent BBC interview he described his excitement at finally being able to run for his country.

"To stand on the start line wearing a South Sudan vest would be amazing," he said.

"A lot of people lost their lives for the freedom of the country we have now. That's what I run for and that's the reason I want to represent the flag."

The 32-year-old marathoner was born in a southern village at the start of the war, which claimed eight of his siblings.

When he was a boy his parents sent him to live with an uncle in Khartoum because it was safer. But it took him three years to get there. He ran away from refugee camps and at one point was abducted and forced into servitude for a soldier's family.

Marial eventually fled Sudan in 1999 after a night-time attack by Sudanese soldiers on his uncle's home. He was knocked unconscious when a soldier smashed his jaw with a rifle.

He escaped first to Egypt before moving to the US when he was 16.

In the lead-up to London, Olympic chiefs suggested Marial compete for Sudan but he refused, saying it would be a betrayal of his country, his family and everyone who fought for independence.

Marial returned to his parents' home in US after the London Games. His parents were reunited after two decades apart.

"It was overwhelmingly emotional," Marial told the BBC. "My mom almost walked past me because she didn't know who I was. Someone shouted and that's when she saw me and collapsed out of shock.

"I knelt down, hugged her and lifted her up. She kept tapping me and saying, 'Is it you, is it you?'."

Although Marial has a personal best time just shy of 2 hours and 13 minutes, he almost never made Rio.

In the Ottawa marathon in May a motorbike he was following on the course took a wrong turn, meaning he ran extra miles, missing the qualifying time for Rio.

The chemistry graduate, also known as Guor Mading Maker, tried again to qualify at Australia's Gold Coast marathon in early July but collapsed before finishing.

Marial's Olympic dreams appeared over, but world athletics chiefs stepped in at the last minute to secure him a spot in Sunday's race, which starts from Rio's carnival grounds.

He and his two teammates are not the only South Sudanese at Rio. Five others have been competing as part of the Olympics' first refugee team which was set up to raise awareness of the global refugee crisis.

The five runners were picked from Kenya's huge Kakuma refugee camp, home to many South Sudanese.