Jung Wook Jin, known professionally as Nine, is a South Korean singer, dancer, composer, actor, and member of ONLYONEOF (온리원오브). He graduated from Gyeonggi High School and later obtained a bachelor's degree in Cosmetics and Beauty from Semyung University.

He made his debut in May 2019 as the group's vocalist and maknae with their first mini-album, "Dot Point Jump". Their agency, 8D Entertainment (에잇디엔터테인먼트), wanted them to have the concept of being "ubersexual" (meaning mixing sexiness and masculinity with a hint of softness). They trained for three years, coming up with songs, stage compositions, costumes and concepts themselves for the weekly evaluations. Billboard named them one of the K-pop rookie groups to watch in 2020.

In April 2021, they faced some controversy when they released the single "Libido", part of their third mini album "Instinct Part. 1". He and KB were in charge of composing the song, and it dealt with sexual instinct and desires, something rarely explored by a South Korean idol group. The choreography was deemed too suggestive by some music critics as the members touched each other's bodies and used strings. However, the song was chosen as the best Korean music video of 2021 by Rolling Stone India for breaking boundaries and representing the LGBTQ+ community.

In November 2023, the whole group was cast in the BL drama "Bump Up Business". One month later, he was introduced as the group's new leader after the position was left vacant after Park Ji Sung's (formerly known as Love) departure back in August 2021. They spent most of 2024 on an international tour.

(Source: kisskh) Edit Biography