Koki Tanaka (田中聖, Tanaka Kōki, born November 5, 1985) is a Japanese singer–songwriter, actor and former Japanese idol, he was a member of Jpop idol boy band KAT-TUN from their debut until September 30, 2013 when his contract with Johnny & Associates (the company that manages KAT-TUN) was terminated. When he was a member of KAT-TUN, he was recognized as the rapper in the group and has a hip-hop-influenced style.