Lee Soon-kyu, also known by her Western name, Susan Soon-kyu Lee and known professionally as Sunny (써니), is an American-born South Korean singer, actress, and radio host. She is a member of Kpop girl group, Girls' Generation, as a lead vocalist.

Sunny was born on May 15, 1989 in Orange County, California, and moved to Kuwait while she was still an infant. Her family moved to South Korea around the time of the Gulf War. She has two older sisters, who share the same birthday as her but were born in different years. She is the niece of Lee Soo Man, the founder of SM Entertainment. In 1998, Sunny entered Starlight Entertainment and became a trainee for 5 years before transferring to Starworld where she became a member of a duet called "Sugar" which never debuted. One of her older sisters was the manager for Sugar, but when the group disbanded, she became active in other parts of the music industry. In 2007, Sunny was recommended by the singer Ayumi Hamasaki to become an SM trainee. After several months of training under SM Entertainment, Sunny made her musical debut as a member of the girl group, Girls Generation, later that year.

Sunny is a graduate of Baehwa All Girls High School.

Sunny made her musical debut as a member of Girls Generation in 2007, she was given the role of a Lead vocalist.

Sunny has contributed to a couple of soundtracks as a solo artist, singing the theme song "You Don't Know About Love" for the SBS drama Working Mom, "Finally Now" for IPTV's Story of Wine and "Your Doll" for the SBS's Oh! My Lady. She featured on the Heading to the Ground soundtrack, singing a duet with Taeyeon in the song SarangInGulYo and another song titled Motion performed with the vocal line of the group. She participated in the S.E.O.U.L. song project along with Super Junior's Kyuhyun, Leeteuk, Ryeowook, Sungmin and Donghae and fellow group members Seohyun, Sooyoung, Jessica and Taeyeon. Sunny featured in Brown Eyed Girls's Miryo's track "I Love You, I Love You" from her first solo mini album, Miryo A.K.A JoHoney.

She was a permanent member on the show Star Golden Bell until Girls' Generation's song Oh! came out. Sunny alongside with Yuri was a part of reality show Invincible Youth in which they were a part of G7, consisting of 7 girls from idol groups. Due to Girls' Generation's Japanese debut and other activities, Sunny left the show, along with Hyuna and Yuri, in June 2010. On October 17, it was confirmed that Sunny would be joining for the second season of Invincible Youth 2, a Korean reality show alongside with Hyoyeon. She is the only returning member from original G7. On July 6, a representative from S.M. Entertainment reported to the media, that Sunny will no longer be a regular casting member anymore alongside the members of G6 from Invincible Youth 2. The unexpected leave will mean that the July 7th episode of Invincible Youth 2, will be the last episode that Sunny will be featured as a permanent member. Sunny's leave does not include fellow Girls Generation member 'Hyoyeon' who will continue as a member on the show.