Kim You-jung (김유정) is a South Korean actress, born in Seoul, who studied at Goyang High School of Arts. She started out as a model for a confectionery brand at the age of 4 and made her acting debut in 2003, quickly becoming one of the most famous and in-demand child actresses in Korea. She was discovered at 5 years old in a contest that her older sister joined and won the Most Popular Award even though she was not one of the official contestants. She is the youngest of three siblings; her older sister, Kim Yeon-jung, is also an actress. Known as "Nation's Little Sister" during her child acting years, she earned the moniker "Sageuk Fairy" after starring in acclaimed historical period dramas such as Dong Yi (2010), Moon Embracing the Sun (2012), and May Queen (2012). In 2016, she successfully transitioned to adult leading roles in the hit period romance Love in the Moonlight. In 2017, she ranked 8th on the Forbes Korea Power Celebrity list, becoming the youngest person ever to enter the Top 10 at 17 years old. In February 2018, she temporarily paused her career after being diagnosed with thyroid dysfunction. She solidified her status as an international star with leading roles in the romantic comedies Backstreet Rookie (2020), Lovers of the Red Sky (2021), and My Demon (2023–2024). Her performance in the popular Netflix retro drama 20th Century Girl (2022) earned her the title "Nation's First Love". Her projects include the Netflix comedy Chicken Nugget (2024), the psychological thriller series Dear X (2025), and the 1930s historical spy romance 100 Days of Lies (2026).

Filmography