Jung Wook Jin, known by his stage name "Nine", is a South Korean singer and dancer managed by 8D Entertainment. He debuted as a member of OnlyOneOf in 2019.

Nine was born in Busan Metropolitan City, South Korea. Around 2015, Nine moved from Busan to Gimhae, South Gyeongsang Province, South Korea, where he studied at Gimhae Gyeongwon High School. In his first year of high school, he tried out for the broadcasting club but was rejected. Instead, Nine was left with auditioning for the dance club, despite having not danced since elementary school. In his third and final year of high school, he was the president of the STEAM (Science, Technology, Engineering, Art & Mathematics) club. In his final year, he transferred to Gyeonggi High School, where he graduated.

In 2016, Nine auditioned in Seoul for BlockBerryCreative, upon the recommendation of a friend from his dance club. On May 28, 2019, Nine debuted as a member of OnlyOneOf with the release of their 1st mini album "dot point jump"