Lee Chang Sun is known by the stage name of Lee Joon. He is currently a singer signed to J.Tune Entertainment, where he is one of the five members of Korean boy band MBLAQ.
Joon was a wig model and actor for CFs. He had a small role in the Korean sitcom That person is coming In 2009 Joon also appeared in Ninja Assassin as a teenage Raizo. He then became a part of the boy band MBLAQ.
After MBLAQ's debut in 2009, Joon was cast as a permanent cast member of a few television shows, including Star Golden Bell Season 2. On February 26, 2010, it was announced that Joon and 7 musicians from 2PM, 2AM and C.N.Blue would be MCs for Mnet M!Countdown.
In 2010, he has been cast in two dramas, titled Jungle Fish 2, in which he will play opposite Ji Yeon from T-ara, and also Stay-at home-mom Kim Kwang Ja a.k.a Housewife Kim Kwang Ja's third activity which aired on the 22nd of September 2010.