Doo Joon is the leader of BEAST. He was a trainee from JYP Entertainment. He was featured in the Mnet documentary Yeolhyeolnama (Korean: 危, Hot Blooded Men) with 2AM and 2PM but was eliminated. He was then transferred to JYP Entertainment's sister company, Cube Entertainment. Before his debut with BEAST, he auditioned for High Kick Through the Roof and was offered a role in the sitcom but turned it down to focus on his music career. He became a member of reality-variety series Danbi, a segment part of MBC's Sunday Sunday Night line-up.
Doo Joon was featured in AJ's music video for "Nunmureul Dakko" (Korean: "覓殊 螻", "Wiping the Tears") as a rapper along with Jun Hyun