BTS, also known as the Bangtan Boys, is a seven-member South Korean boy band that began formation in 2010 and debuted in 2013 under Big Hit Entertainment. The septet-composed of Jin, Suga, J-Hope, RM, Jimin, V, and Jungkook-co-writes and co-produces much of their own 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 and coming-of-age, 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 released several albums and performed on several world tours. After debuting in 2013 with their single album 2 Cool 4 Skool, BTS released their first Korean-language studio album, Dark & Wild, and Japanese-language studio album, Wake Up, in 2014. The group's second Korean studio album, Wings, was their first to sell one million copies in South Korea.