Yook Sung-jae, also known mononymously as Sungjae, is a South Korean singer, songwriter, actor, host and entertainer. He is a member of the boy group BtoB and its sub-group, BtoB Blue. Aside from his group's activities, Yook has acted in television dramas Reply 1994 (2013), Plus Nine Boys (2014), Who Are You: School 2015 (2015), The Village: Achiara's Secret (2015), Guardian: The Lonely and Great God (2016), Mystic Pop-up Bar (2020) and The Golden Spoon (2022). He has appeared in several reality shows, including: Hitmaker, We Got Married, and Master in the House.

Reply 1994 is a 2013 South Korean television series starring Go Ara, Jung Woo, Yoo Yeon-seok, Kim Sung-kyun, Son Ho-jun, Baro, Min Do-hee, Sung Dong-il, and Lee Il-hwa. It aired on tvN from October 18 to December 28, 2013 for 21 episodes.