Lee Ji-eun (Korean: 이지은; born May 16, 1993), also known by her stage name IU (아이유), is a South Korean singer-songwriter 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 Lost and Found (2008), her first EP. Although her follow-up albums in 2009, Growing Up and IU...IM, brought mainstream success, it was only after the release of "Good Day", 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.

With the success of her 2011 albums, Real+ and Last Fantasy, IU established herself as a formidable force on the music charts of her native country and further cemented her girl next door image as Korea's "little sister". 2011 also saw her first foray into songwriting with "Hold My Hand", which was written for the television series The Greatest Love. IU's third studio album, Modern Times (2013), showcased a more mature musical style that marked a departure from her earlier girlish image, with several tracks reaching the top 10 on the Gaon Digital Chart. The album was ranked number two on Billboard's "25 Greatest K-Pop Albums of the 2010s" list. IU subsequently exerted more creative control over her music; Chat-Shire (2015) marked the first time she was credited as the sole lyricist of her own album. IU's fourth studio album, Palette (2017), became her first to reach number one on Billboard's World Albums chart. While her following records Love Poem (2019) and Lilac (2021) continued to deviate from mainstream K-pop styles, exploring and mixing various music genres, IU consistently retained her dominance on South Korean music charts. Her 2020 single "Eight" (prod. by Suga) became her first to reach number one on Billboard's World Digital Song Sales chart.

Aside from her music career, IU has ventured into acting and hosting radio and television shows. Following her supporting role in the hit teen series Dream High (2011), she was cast in leading roles in melodrama You Are the Best! (2013), romantic comedy Bel Ami (2013–14), comedy drama The Producers (2015) and historical fiction Moon Lovers: Scarlet Heart Ryeo (2016). IU's role as a desperate office worker in My Mister (2018) received critical acclaim, and she earned her first Best Actress in Television nomination at the 55th Baeksang Arts Awards. In 2019, she starred in anthology film series Persona and dark fantasy Hotel del Luna, the latter of which led to her second Best Actress nomination at the 56th Baeksang Arts Awards. In 2022, IU starred in Hirokazu Kore-eda's film Broker alongside Song Kang-ho, Bae Doona and Gang Dong-won.

IU has released a total of five studio albums and nine EPs, five of which have reached number one on the Gaon Album Chart, and thirty number-one singles, making her the artist with the most number-one songs in South Korea. One of the best-selling solo acts in the group-dominated K-pop industry, IU became the first solo female K-pop act to perform at the Olympic Gymnastics Arena during the Seoul leg of her 2018 dlwlrma concert tour for her 10th anniversary and also the first Korean female artist to hold a solo concert, The Golden Hour, at Seoul Olympic Stadium in Seoul on September 17 and 18, 2022. Rolling Stone named her the 135th greatest singer of all time in a 2023 ranking. She has been included five times in the top ten of Forbes magazine's annual Korea Power Celebrity list since 2012 and attained a peak ranking of number three that year. In 2014, Billboard recognized IU as the all-time leader of its K-pop Hot 100 with the most number-one songs and the artist with the most weeks at the number-one position on the chart. She was named Gallup Korea's Singer of the Year in 2014 and in 2017.