BTS, also known as the Bangtan Boys, is a seven-member South Korean boy band who began formation in 2010 and debuted in 2013. The septet co-writes and produces much of their output. Originally a hip hop group, their musical style has evolved to include a wide range of genres. Their lyrics, often focused on personal and social commentary, touch on the themes of mental health, troubles of school-age youth, loss, the journey towards loving oneself, and individualism. Their work features references to literature and psychological concepts and includes an alternative universe storyline. The group has staged several world tours.