Viktor Ahn, the athlete who has won the most Olympic gold medals in short track speed skating history, announced his retirement on Monday.

In a letter published by RIA Novosti news agency, the six-time Olympic champion said constant knee pain together with other injuries were behind his decision to retire.

"It's becoming more and more difficult to keep fit, so I decided it was time to leave the big sport."

"I came to the conclusion that it is impossible to pursue a sports career on motivation alone. I think that this is the right time, so I decided to retire," he added.

Severe knee injury after Turin

Born Ahn Hyun-soo, Ahn was once the pride of South Korea's winter sports. He won the world junior short track championship in 2002 at the age of 17 and participated in the Salt Lake City Winter Games the same year.

At the 2006 Turin Winter Olympics, the 21-year-old amazed the world by winning gold medals in the 1,000 meters, 1,500 meters and 5,000-meter relay, as well as a bronze medal in the 500 meters, making him the most decorated athlete at the Games and a national hero for South Korea.

After Turin however, Ahn sustained a severe left knee injury. He underwent four injuries in one year and took 15 months to recover leading up to the next Olympics. Because of the injury setbacks, and a lack of support from South Korea's skating authorities, Ahn was passed over for Vancouver.

South Korea's focus on winning gold medals as well as the factional infighting in the South Korean national team made Ahn feel he was no longer wanted, even after he fully recovered from his injuries.

During that time, Russia made Ahn a generous offer as it was seeking to become a contender in the sport as it geared up to host the Sochi Games. In 2011, Ahn moved to Russia to train and later became a naturalized Russian athlete. Ahn has represented Russia ever since.

No pain, no gain

In 2011, Ahn and his wife Woo Nari moved from Seoul to Moscow and kicked off a journey filled with loneliness and frustrations in the beginning.

HIs first training session with the Russian team disappointed everyone. Having just completed his fourth knee surgery and not being able to receive systematic training for more than a year, Ahn was outcompeted by female skaters at the time.

Making the situation more difficult was the language barrier he had to overcome and the unfamiliar Russian life he and his wife needed to adapt to.

However, compared to the fierce competition South Korean speed skaters had to face, Ahn was given more time to recover from his injuries and find his form back in Russia.

At the 2014 Winter Olympics in Sochi, Ahn returned to the pinnacle of his sport, winning gold medals in the 500 meters, 1,000 meters and the 5,000-meter relay as well as a bronze in the 1,500 meters.

The helmet he wore in Sochi was custom made before he came to Russia in 2011. On the helmet it said "no pain no gain."

With six Olympic golds and two bronzes, Ahn surpassed China's Wang Meng, who has six Olympic medals, including four golds, to become the most decorated Olympian in short track history.

Missing the 2018 Pyeongchang Winter Games

Ahn didn't make the list of Russian athletes eligible to compete at the Pyeongchang Winter Games in 2018, after the International Olympic Committee (IOC) banned Russia from Pyeongchang over "systematic manipulation" of the anti-doping system at the 2014 Sochi Games.

He wrote an open letter to IOC President Thomas Bach, insisting he was in strict compliance with anti-doping legislation and demanded an explanation for his ban. 

Never being publicly implicated in any doping cases, Ahn said, "It is outrageous that there is no concrete reason which explains my exclusion from the Olympics" in the letter. 

Ahn's exclusion from Pyeongchang shattered his hope of competing at one more Olympics given the fact that he will turn 37 years old by the 2022 Beijing Winter Games and Russia was banned again from major international competitions by the World Anti-Doping Agency due to the country's doping non-compliance. 

Ahn missed the 2020 World Short Track Speed Skating Championships due to be held in Seoul in March after the competition got canceled over the coronavirus pandemic.

He competed in his last race at a simulation world championship held by China's short track speed skating national team in Beijing last month.

In his farewell letter, Ahn concluded by thanking Russian Skating Union President Alexey Kravtsov, Russian athletes and fans. "Wherever I am, I'll always do my best to develop the sport, but part of my soul will remain in Russia."