El grupo debutó en 2003 como un grupo de 5 miembros que consistió en el líder U-Know Yunho (유노윤호 ユンホ), Max Changmin (최강창민 チャンミン), Hero Jaejoong (영웅재중 ジェジュン), Micky Yoo Chun (믹키유천 ユチョン) y Xiah Junsu (시아준수 ジュンス).
En julio de 2009 Jaejoong, Yoochun y Junsu presentaron legalmente una demanda judicial en contra de su agencia coreana SM Entertainment.
Kim made his debut in 2003 as a member of TVXQ, a boy band produced and formed by South Korean record label and talent agency S. Entertainment, having previously been a trainee for six years.
Tras una pausa que duró 2 años y 3 meses, TVXQ volvió como un dúo formado por Yunho y Changmin.) or simply U-Know, is a South Korean singer, actor, and a member of the pop duo TVXQ. After over two years of training, Yunho debuted with TVXQ in December 2003.Born and raised in Gwangju, South Korea, Yunho auditioned for the Korean talent agency S. TVXQ have released fifteen studio albums and performed on record-breaking concert tours; their sixth Japan-wide tour, the Time Tour, was the highest-grossing concert tour ever held by a foreign music act in Japan.His family, who suffered greatly from the 1997 Asian financial crisis, were initially against his decision to become a singer.In order to provide for himself while he trained in Seoul, Yunho took up various part-time jobs in the city, such as working snow removal in the morning and as a waiter at night.