AJ debuted with his single album "First Episode: A New Hero" and promoted with the song "Dancing Shoes". His first ever debut stage was April 4, 2009 on M!CountDown. Before AJ debuted, he was trained in JYP Entertainment for 4 years and was transfered to Cube Entertainment. AJ finished promotion of his album with the song "눈물을 닦고" (Wipe The Tears). AJ has now been transferred to the boygroup B2ST who debuted October 2009.