Ryeowook was discovered through the CMB Youth ChinChin Festival in 2004 and signed a contract with SM Entertainment soon afterwards after impressing judges with his singing talent. Trained in areas of singing, dancing, and acting, Ryeowook placed particular efforts into his vocal training and music composition. He plays piano, and play accompaniment for fellow members during their solo stages at their concerts.
Before Kyuhyun was added in 2006, Ryeowook was the last to join Super Junior several weeks before their official debut in 2005. Having undergone only two months of training, Ryeowook's late addition was rumored to be a replacement of a previous SM trainee that was supposed to debut as a member of Super Junior 05, the first generation of Super Junior.