Kōki Tanaka (田中聖) (b. November 5, 1985 in Chiba, Japan) is a Japanese rapper/singer-songwriter, actor, television personality and radio host. He joined Johnny & Associates in 1998 and became a member of the popular J-pop group KAT-TUN in 2001. Kōki is the second T in the group's name. The group officially debuted in 2006 and has since achieved an unbroken streak of success with all five albums and thirteen singles debuting at number 1 on the Oricon charts.