Lee Su-ji (Korean: 이수지; born March 20, 1998), also known mononymously as Suji and Halla, is a South Korean singer and actress. She debuted as a member of the South Korean girl group The Ark and later was a member of the project girl group UNI.T. She was also a member of Real Girls Project as part of her acting role in The Idolmaster KR.

Lee Su-ji was born on March 20, 1998, in Busan, South Korea. She grew up in Daegu, South Korea.^[1] She attended Hanlim Multi Art School learning Broadcasting & Entertainment Department in Seoul^[2] and graduated on 10 February 2017. She joined Music K Entertainment in 2013 and trained for two years.

In 2014, Lee appeared in the music video of labelmate Hong Jin-young's song "Cheer Up".^[3] On April 12, 2015, she debuted as a member of Music K Entertainment's new girl group The Ark under the stage name "Halla".^[4][5] The group released one single, "The Light", before going on hiatus. In March 2016, it was unofficially announced that the group had disbanded a month before. On April 26, 2016, Lee joined the auditions for The Idolmaster KR, a Korean drama loosely based on the Japanese raising simulation and rhythm video game series The Idolmaster,^[6] where she played the main lead and her twin sister.^[7] On August 25, she debuted as a member of girl group Real Girls Project, which was formed for the drama.^[8][9] On November 4, 2017, Lee joined The Unit: Idol Rebooting Project.^[10][11][12] She won a final spot on Top 9 and became a part of the group called UNI.T.^[13][14]

On September 5, 2023, Lee announced her engagement to her boyfriend through Instagram.^[15] Lee and actor Ko Hyoung-woo married on October 7, 2023, in Seoul.^[16]