Yook Sung-jae (Korean: 육성재; Hanja: 陸星材; born (1995-05-02)May 2, 1995), better known mononymously as Sungjae, is a South Korean singer, songwriter, actor, and entertainer. He is a member and the third generation leader of the boy group BtoB and its sub-group, BtoB Blue. Aside from his group's activities, Yook has acted in television dramas Who Are You: School 2015 (2015), The Village: Achiara's Secret (2015), Guardian: The Lonely and Great God (2016) and Mystic Pop-up Bar (2020) and has appeared on hit shows like Hitmaker, We Got Married and Master in the House.