B1A4 (Hangul:비원에이포) is a South Korean boy group formed by WM Entertainment . The group debuted on April 23, 2011 with the single "O.K" from the EP Let's Fly , after being introduced to the public through a webtoon . They have released seven studio albums (three Korean and four Japanese) and seven EP s, as well as four compilation albums. The group has had considerable commercial and critical success in both the Korean and Japanese markets. They have also toured in the United States.