BOL4 (also known as Bolbbalgan4 (볼빨간사춘기)) is a South Korean one-member act under Shofar Music. They debuted as a duo on April 22, 2016 with their first mini album Red Ickle.
On April 2, 2020, Shofar has announced that Woo Ji Yun has departed from BOL4, with An Ji Yeong to continue to promote under the duo's name, without any additional members.
Ji Yeong and Ji Yun became friends in high school in Yeonju, Gyeongsangbuk-do. They then started a four-member band together and later participated on the reality competition show Superstar K6. After the show, Ji Young and Ji Yoon received contract offers from various agencies before settling with Shofar Music.