Choi Yeon-jun, better known by the mononym Yeonjun, is a South Korean singer-songwriter born on September 13, 1999, in Seongbuk District, Seoul, South Korea. He trained under Big Hit Entertainment for four years and was known as the company's "legendary trainee" due to his consistent top rankings in dance, vocal performance, and rap during monthly evaluations. Yeonjun is a member of the boyband Tomorrow X Together, which debuted in March 2019. Yeonjun has also been involved in various projects outside of Tomorrow X Together. He made his acting debut in the 2020 television series Live On. In 2021, he participated in New York Fashion Week as a model for a South Korean brand and featured on Enhypen's first studio album Dimension: Dilemma in 2021. He also collaborated with American singer-songwriter Salem Ilese on the single "PS5" alongside his bandmate Taehyun and Norwegian DJ Alan Walker in 2022. His contribution to the original soundtrack of the television series Cinderella at 2 AM with the song "Boyfriend" was released on September 1, 2024, before his official solo debut with the single "Ggum" on September 19, 2024.