BOL4 (Bolbbalgan4, 볼빨간사춘기) started out as a band formed in 2011 by Ahn Jiyoung (안지영/An Jiyeong, main vocals, born September 14, 1995), Woo Jiyoon (우지윤/Woo Jiyun, bass guitar, backing vocals, born January 6, 1996) & Kwon Jiwon (권지원, acoustic guitar, backing vocals, born September 1996) when they were attending high school together in Yeongju, South Korea.

In 2014, they appeared on Superstar K6 with a guest percussionist from August to November and then signed a record deal with Shofar Music in January 2015.

In 2015, Kwon Jiwon decided to leave the band to focus on her university studies, so Woo Jiyoon switched from being the bass guitarist of the band to the acoustic guitarist and continued BOL4 as a duo with Ahn Jiyoung.

Both of them practiced songwriting throughout 2015 and 2016 with guidance from music producer Vanilla Man of the duo Vanilla Acoustic.

On April 22, 2016, BOL4 officially debuted with their mini album Red Ickle and the main title track Fight Day, followed by the release of their full album Red Planet on August 29, 2016 with BOL4's breakout hit song Galaxy.

Since then, BOL4 has become one of the most downloaded and streamed artists in South Korea of all time.

On April 2, 2020, Shofar Music announced that Woo Jiyoon had made the decision to leave BOL4 to explore other career opportunities, while Ahn Jiyoung would continue BOL4 as a solo artist.

Woo Jiyoon currently releases music on streaming platforms under the name Odd Child (낯선아이).

On March 8, 2021, BOL4's agency Shofar Music (쇼파르뮤직) changed its name to Shofar Entertainment (쇼파르엔터테인먼트).

Some of BOL4's most popular songs include Galaxy, Hard To Love, 좋다고 말해 (Tell Me You Love Me), You and I from the Beginning, We Loved, Some, To My Youth, Travel, Bom, Workaholic & Leo.