Name: f(x) (에프엑스) Debut: September 5, 2009 Debut Single: "La chA tA" Members: Victoria, Amber, Luna, Krystal Former Members: Sulli f(x) is a four member girl group signed under the Korean record label SM Entertainment. The group debuted in 2009 and has been repeatedly acknowledged for their eclectic electro-pop sound. Originally a five member group, f(x) currently consists of four members: Victoria, Amber, Luna, and Krystal. f(x) debuted with five members (Victoria, Amber, Luna, Krystal, and Sulli) on September 5, 2009 with a pop dance single entitled "La chA tA." The group followed up their debut with the release of a second single entitled "Chu~♡," followed by the release of their first EP, Nu ABO in May of 2010. The next month, Amber went on an extended hiatus due to an ankle injury, while the group to promoted as four without her. f(x) released their first full-length album Pinocchio in 2011, which they later re-packaged with "Hot Summer" as the lead single. "Hot Summer" went on to become one of the biggest singles of Summer 2011, selling nearly 3 million copies by the end of the year. The group dropped their critically-acclaimed second EP Electric Shock in June of 2012. The album's lead single "Electric Shock" won the group multiple weekly and year-end awards. In March of 2013, f(x) became the first ever Kpop group to perform at the SXSW music conference in Austin, Texas. Later that summer, the group released their second full-length album Pink Tape, promoting a lead single entitled "Rum Pum Pum Pum." The album was a success not just in Korea, but in the United States as well, peaking at #1 on the Billboard World Albums chart. In July 2014, f(x) released their third full-length album Red Light, but promotions for the album were cut short when Sulli went on an abrupt hiatus from the entertainment industry, citing mental and physical exhaustion from malicious comments and rumors online. In August, it was officially announced that Sulli would be leaving the group to focus on her acting career. Though she no longer promotes with f(x), she is still signed under SM Entertainment. The remaining members of f(x) continue to promote together, and released their first album as a four member group -- 4 Walls -- in October of 2015.