BTS, also known as the Bangtan Boys, is a South Korean boy band formed in 2010 and debuting in 2013 under Big Hit Entertainment. The septet—consisting of members Jin, Suga, J-Hope, RM, Jimin, V, and Jungkook—co-writes and co-produces much of their own material. Originally a hip hop group, their musical style has evolved to incorporate a wide range of genres; their lyrics have often discussed mental health, the troubles of school-age youth and coming of age, loss, the journey towards self-love, and individualism. Their work also frequently references literature, philosophy and psychological concepts, and includes an alternate universe storyline. After launching in 2013 with their single album 2 Cool 4 Skool, BTS respectively 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.