Seo first appeared internationally in February 2011 at the Junior World Championships in Courmayeur . There he won the silver medal over 1000 m and the gold medal over 1500 m, in the all-around and in the 1500 m superfinal. He made his debut in the World Cup in Nagoya in December 2011 , finishing sixth over 500 m and third over 1000 m. At the beginning of the 2014/15 season he won his first World Cup victory in Salt Lake City over 1000 m. In the further course of the season he won the World Cup twice with the relay and once 500 m. His best results at the 2015 World Championships in Moscow were fifth in the 1000 m and fourth in the relay. At the Winter Universiade 2015 in Granada , he won the silver medal over 1000 m and the gold medal over 500 m. In the 2015/16 season he finished in the World Cup in Toronto over 1000 m and second place with the relay and won his fifth World Cup victory in Dresden over 1500 m. At the season highlight of the 2016 World Championships in Seoul , he won the bronze medal with the relay. In addition, he was ninth over 1500 m, eighth in the all-around and fourth over 500 m, 1000 m and 3000 m. He finished the season in eighth place in the overall world cup over 1000 m and in seventh place in the overall world cup over 1500 m. In December 2016 he finished third with the relay at the World Cup in Shanghai . At the 2017 World Championships in Rotterdam , he won the bronze medal over 500 m and 1500 m, the silver medal over 3000 m and the gold medal over 1000 m and in the all-around event. In February 2017 he won at the Winter Asian Games in Sapporo over 500 m and with the relay the silver medal and over 1000 m the gold medal. In the 2017/18 World Cup season he achieved third place over 1000 m in Dordrecht and second place over 500 m and with the relay in Shanghai. In Seoul, he won the relay and finally achieved seventh place in the 1500 m World Cup and sixth place in the 500 m World Cup. At the highlight of the season, the 2018 Winter Olympics in Pyeongchang , he won the bronze medal in the 1000 m and also achieved fourth place in the relay. At the 2018 World Championships in Montreal , he won the gold medal with the relay. In the all-around competition he ran there on the 13th place.
Note: This article places the family name before the person's first name. This is the usual order in Korean. Seo is the family name here, Yi-ra is the first name.
South Korea
