<noinclude> </noinclude> BOL4 (), also known as Bolbbalgan4 or , is a South Korean musical act formed by Shofar Music in 2016. They appeared on Superstar K6 in 2014 before signing a contract with their current agency. BOL4 was originally a duo consisting of Ahn Ji-young and Woo Ji-yoon. They debuted with the single "Fight Day" from the mini-album Red Ickle on April 22, 2016.
The duo went on a temporary hiatus due to Ahn's music classes requirements in the first half of 2018. BOL4 signed with King Records and debuted in Japan on June 5, 2019, with the mini-album Red Planet (Japan Edition).
On April 2, 2020, Shofar Music announced that Woo Ji-yoon had left the duo and that Ahn Ji-young will continue to promote as BOL4. In April 2025, BOL4 parts ways with their agency after 10 years of working with them.
The group's name in English comes from the first syllable of the Korean word ("puberty"), which is pronounced the same as the Sino-Korean numeral four ().
Ahn Ji-young and Woo Ji-yoon were both raised in Yeongju, North Gyeongsang Province, and were classmates. They had previously competed on Superstar K 6 in 2014. Since they were young, they had dreamed of becoming singers. The name of their duo was chosen because they wanted to make the kind of pure, honest music that can only be found in adolescence. Woo portrays the "blushing" part of the name because she is often shy, while Ahn portrays "youth" because she acts like an adolescent girl.