Who Was Yoo Ji-won? South Korean Running Influencer Dies After Collapsing During Seoul Half-Marathon

Yoo Ji-won, a 25-year-old graduate researcher and running content creator, has died after collapsing about 500 metres from the finish of a half-marathon in Seoul, South Korea. She was taking part in the 2026 Seoul Race on 11 October when she suffered a medical emergency.

Yoo researched artificial intelligence semiconductors at the Korea Advanced Institute of Science and Technology (KAIST) and documented her training and race achievements online. Organisers said the runner received emergency treatment before being taken to a medical facility, where she subsequently died. The cause of her collapse and death has not been publicly disclosed.

Who Was Yoo Ji-won?

Yoo was a graduate student at KAIST, where she researched AI semiconductors. Alongside her academic work, she shared her experiences as a runner on Instagram under the account @mta1n_0ne.

Her posts documented training sessions, race participation and personal milestones. She took up running in 2022 and began pursuing faster times more seriously in the summer of 2025, according to South Korean reporting.

In a March interview on a running YouTube channel, Yoo described a routine built around her laboratory work. VnExpress, citing South Korean newspaper Munhwa Ilbo, reported that she would arrive at the lab at 9am and run for about two hours from 8pm, sometimes returning to the lab afterwards if work remained.

Her race results reflected the progress she had made. On 15 March 2026, Yoo completed the Seoul Marathon in two hours, 56 minutes and 32 seconds, finishing the full marathon in under three hours.

The following month, she won the women's 10-kilometre masters category at the Gunsan Saemangeum Marathon, according to South Korean media reports.

What Happened to Yoo Ji-won During the 2026 Seoul Race?

The Seoul Race Organising Committee said a participant in the half-marathon collapsed at the 20.6-kilometre mark at approximately 8.49am on 11 October. That placed the incident about 500 metres before the finish of the 21.0975-kilometre course.

According to the Seoul Metropolitan Government, which hosts the race, an official who found the runner near Gwancheol-dong in Jongno District called emergency services and performed CPR.

The participant received emergency treatment before being transported by ambulance to a nearby hospital, where she later died. Subsequent reports identified her as Yoo.

The event began at Seoul Plaza at 7.30am and offered half-marathon and 11-kilometre courses. Approximately 12,000 runners entered this year's race.

In a statement published on 12 October, the organising committee offered condolences to the runner's family and acknowledged the distress felt by other participants. It said it would closely examine the incident and take necessary follow-up measures.

No medical explanation for Yoo's collapse has been made public.

Yoo Ji-won's Final Instagram Update Draws Emotional Tributes

Yoo's last reported Instagram update, posted on 4 October, featured her result from a recent 10-kilometre run. Following news of her death, friends, followers and fellow runners left messages remembering her achievements and enthusiasm for the sport.

One commenter recalled watching her running videos and regarding her as an amazing runner, adding that they would remember her for a long time.

Her friend and fellow running content creator Bummy also shared a tribute. In a Korean-language post translated by People, he described seeing a crowd gathered near the finish and initially thinking someone had been hurt.

After crossing the line, he looked for Yoo near the awards podium before learning what had happened. He said he rushed to the hospital, hoping to see her one last time.

'I am so sorry I couldn't stay by your side until the very end,' he wrote.

His account described learning of the emergency after finishing his own race, rather than witnessing Yoo's collapse. Her social media posts have since become a place for fellow runners and followers to share condolences and remember the training and achievements she documented.