A jazz-trained vocalist, KATIE launched her career as a K-pop hitmaker by winning the fourth season of K-Pop Star in 2015. She was born as "Kim Seo-hyeon" in Bucheon, South Korea, on December 10, 1993, and relocated to New Jersey at 10 years old. Although she briefly studied jazz at Berklee School of Music, she ultimately dropped out due to budget constraints and, instead, auditioned for the reality television show K-Pop Star 4 in 2014. After passing the competition's preliminary auditions that summer, she earned a spot in the show itself, appearing in weekly episodes throughout the latter half of 2014 and the early part of 2015. As a member of the show's Top 10, she released the single "Where You Need To Be" on the compilation album K-pop Star Season 4 Top 10. The song peaked at Number 5 on South Korean's GAON Music Chart, and KATIE signed with YG Entertainment after winning the show in April 2015. Work on her debut album proved to be slow, however, and she eventually left YG's roster to sign with AXIS instead. "Remember," her debut single for the label, was released in 2018 and became a viral hit, earning more than 10 million views for its music video. "Future Love," a remix of "Remember" featuring Ty Dolla Sign, and "Thinkin Bout You" followed in 2019, with all three tracks also appearing on her debut EP, Log.