Lee Ji-eun (Korean: 이지은; born May 16, 1993), also known by her stage name IU (Korean: 아이유), is a South Korean singer-songwriter, record producer, and actress. She signed with LOEN Entertainment (now Kakao Entertainment) in 2007 as a trainee and debuted as a singer at the age of fifteen with her first extended play (EP) Lost and Found (2008). Although her follow-up albums, Growing Up and IU...IM, brought mainstream success, it was only after the release of "Good Day" (Korean: 좋은 날), the lead single from her 2010 album Real, that she achieved national stardom. "Good Day" went on to spend five consecutive weeks at the top of South Korea's Gaon Digital Chart, and in 2019, it was ranked number one on Billboard's "100 Greatest K-Pop Songs of the 2010s" list.

Lost and Found is the debut extended play (EP) by South Korean singer-songwriter IU. It was released by LOEN Entertainment on September 23, 2008. IU collaborated with lyricist and producer Choi Gap-won, who had previously produced songs including "Amnesia" by Gummy, "Incurable Disease" by Wheesung, and "Toc Toc Toc" by Lee Hyori. Lee Jong-hoon of Soul-Shop and the singer Mario additionally worked on the title song, "Lost Child".
Given a reference text about a singer, tell me when they debuted, what their first release was, and what their most popular song is.
The singer Lee Ji-eun, or better known as IU, debuted on September 23, 2008 with her first extended play "Lost and Found". Her most popular song is "Good Day" from her 2010 album "Real" which was ranked number one on Billboard's "100 Greatest K-Pop Songs of the 2010s" list.