Yoon Byung Ok, later legally changed to Yoon Ji Sung, is a South Korean singer, dancer, actor, and former member of WANNA ONE (워너원). He graduated from National Traditional Arts High School and later obtained a bachelor's degree in Theater and Film from Myongji College and a master's degree in Performing Arts from Dongguk University. Before debuting, he was a trainee at MMO Entertainment and served as a backup dancer of FIESTAR member Cao Lu. In mid-2017, he participated in the survival competition "Produce 101 Season 2" and managed to end up in 8th place, earning a spot in the resulting project group. He made his debut in August 2017 as WANNA ONE's leader and sub-vocalist with their first mini-album, "1X1=1 (To Be One)". The contract with Swing Entertainment (스윙엔터테인먼트) was made for one year and six months, so the group officially disbanded in January 2019 following their final concert performance. He made his debut as a solo artist in February 2019 with the mini-album "Aside". He then enlisted for his mandatory military service on May 14, 2019, and was discharged on December 13, 2020. After serving, he made his acting debut in November 2021 with a role in the SBS drama "Let Me Be Your Knight". He is now represented by Billions (빌리언스).