Cho Kyu-hyun, referred to as Kyuhyun, is a South Korean singer, musical theatre actor and television host. He debuted as a new member of boy group Super Junior in May 2006. Apart from his group's activities, he has established himself as a musical actor, notably through his participation in the original and Korean versions of stage musicals including The Three Musketeers, Catch Me If You Can, Moon Embracing the Sun, Singin' in the Rain, The Days, Robin Hood, Werther, Mozart!, The Man Who Laughs, Phantom, and Frankenstein. He was also cast in television shows including Radio Star, We Got Married, Mamma Mia, Fluttering India and in the third, fourth, seventh, and eighth seasons of New Journey to the West. He debuted as a solo artist with his debut mini album, At Gwanghwamun, on November 13, 2014, making him the first Super Junior member to debut as a solo artist.

"U" is a song recorded in multiple languages by South Korean boy group Super Junior, with the original Korean version released through SM Entertainment on May 25, 2006. A CD single was released in South Korea on June 7 and peaked at number one on the monthly MIAK album chart in June 2006, selling copies over 83,000 by July 2007. The song won five first place awards on South Korean music programs.