B1A4 is a boy group under WM Entertainment. They debuted on April 23, 2011 on MBC's Show! Music Core performing "O.K" from their first mini-album Let's Fly. The group's name has dual meanings: the member's blood types and 'Be the one, All for one'.
On June 30, 2018, Jinyoung and Baro left WM after deciding not to renew their contracts. The three remaining members renewed and will continue to promote as a trio, with the possibility of five-member group activities in the future.