Kim Ju-sung is a South Korean left-footed centre-back born in Cheongju on 12 December 2000. He came through FC Seoul's youth system and joined the senior team in 2019, making his K League 1 debut the same year. After a military-service spell with Gimcheon Sangmu, he returned to FC Seoul and later moved to Sanfrecce Hiroshima. Kim represented South Korea at the 2019 FIFA U-20 World Cup and became part of the senior national team pool in the 2020s, adding a left-footed option in central defence.