AOA (an acronym for Ace of Angels; Korean: 에이오에이) is a South Korean idol girl group and band, produced by FNC Entertainment. These groups are constructed of a band with 5 members (Choa, Jimin, Yuna, Yookyoung and Mina), and an idol group consisting of 7 members (all members excluding Youkyoung). The groups debuted on July 30, 2012, with their single album Angel's Story.

The eight members were introduced individually through eight different teaser photos released from July 16, 2012 to July 23, 2012 (in order: Seolhyun, Choa, Hyejeong, Chanmi, Yuna, Mina, JiMin & Youkyoung (Y)). AOA was revealed to be a dance group, with some members also playing instruments. Youkyoung (or "Y") is listed as a "half-angel/half-mortal", because she is only a member of the band half, playing the drums, resulting in AOA saying they are a "7+1" group. Explaining the concept of their debut FNC revealed that the seven "full angel" members (Seolhyun, Choa, Hyejeong, Chanmi, Yuna, Mina, and leader Jimin) looked on the human world through their crystal ball, and fell in love with the music of humanity. Youkyoung, the "half-angel, half-mortal", also referred to as the key keeper, became curious about the human world and used the key to visit it with the other angels. The first music video teaser for "Angel's Story" was released on July 24, 2012 and the second teaser was released on July 26, 2012. "Angel's Story" was leaked on July 28, 2012, with 2 days before the official release. The music video for the title track "Elvis" was released on July 30, 2012. AOA had their debut stage on 9 August on M!Countdown following by Music Bank on 10 August.