Krystal Jung Soo Jung, a Korean American, is one of the members of the Korean girl group f(x). Her older sister is Jessica, a member of the Korean girl group Girls' Generation. She was born in San Francisco, California, USA, and was selected through the SM casting system in 2000. But because she was only six years old at the time, she did not join the company as a trainee until 2006. She debuted as a member of f(x) in September 2009 with Luna as the lead singer of the group.