Lee Chang Sun is a South Korean singer, dancer, model, and former member of 24K and TAN. He graduated from Yangmyung High School and later obtained an associate's degree in Practical Dance from Kookje University. He made his debut in August 2016 when he joined as 24K's new main dancer and vocalist with their digital single, "Still 24K". The group, managed by Choeun Entertainment, was never able to find a steady fanbase and opportunities to promote, often spending several years on hiatus before releasing new material. Plus, the agency began making constant lineup changes starting in 2014. He became the group's leader in January 2019 when Corbyn (formerly known as Cory) left the group. In June 2021, he was part of the digital single "Mainstreet", which ended up being his last collaboration for 24K. Later that year, he entered the singing survival show "Extreme Debut: Wild Idol" and finished in 1st place, earning a spot in a new project group called TAN. He signed a two-and-a-half-year contract with Think Entertainment and re-debuted in March 2022 with their 1st mini-album "1TAN" as the leader, main dancer and sub-vocalist. In September 2023, he officially announced his departure from 24K to focus exclusively on TAN. However, Think Entertainment became embroiled in several controversies, and all members ended their contracts in June 2024. A few weeks later, he announced the group's disbandment and also decided to stop being an idol. He enlisted for his mandatory military service on October 7, 2024, and was discharged on April 6, 2026.