Ki Moon Sung (성기문) is a South Korean Hammond organist and pianist, one third of the organ trio Trio Works with the guitarist Charlie Jung and the drummer Jong Dae Oh (오종대). He is billed Ki Moon Sung on Discogs and on the cover of the trio's album Gunsan Gaka, while Korean press and concert listings print 성기문 and the romanizations vary: Sung Gi-moon, Sung Ki-moon and Seong Gi-mun all turn up. Melon's Music Story feature of April 15, 2013 called him the country's top Hammond organist and one of the five busiest pianists in Korea, and a concert listing in 2024 billed him as Korea's best Hammond organist.

He told Melon that he came to the instrument as a student through Jon Lord of Deep Purple, then found Jimmy Smith and set his heart on becoming a jazz organist. A 2021 cultural magazine from Yeoju adds that he taught himself piano in his teens. No source gives his birth date, his birthplace or his schooling, so the header leaves the birth line open.

The earliest dated trace of him is a Maeil Shinmun notice of August 18, 2004 for a concert by the quartet of the alto saxophonist Hong Soon Dal at the Indigo jazz cafe in Daegu on August 21, with Kim Hyun-il on tenor, Choi Dong-ha on drums, Jo Seong-deok on bass and Sung on piano; the paper describes him as an alumnus of the Kim Su-yeol Jazz Quintet. The Bugs album text for Nouveau Deux (November 25, 2004), a set of jazz arrangements of Korean pop songs, names him as its pianist and an alumnus of the saxophonist Lee Jung-sik's quartet, and lists the rest of the line-up as Jang Gi-ho of the group Bit-gwa-Sogeum (빛과 소금), the bassist Seo Young-do and the Berklee-trained drummer Park Geun-hyuk, with the Japanese guitarist Murayama and saxophonist Suzuki as guests. A year earlier, on the Christmas compilation Winter Story of Jazz Family (Korean Jazz All Star's Edition) (BCS Music, November 29, 2003), he has his own track, "It Came Upon a Midnight Clear".

By 2011 he was leading a Hammond organ trio in the clubs. On March 31, 2011 he closed a ten-night series of Korean jazz concerts at the Munhwa Ilbo Hall in Seoul in a trio with Kim Hyun-il and the guitarist Kang Woong, which the papers called the country's only saxophone and organ trio; Pressian wrote that his name could be found at almost every jazz festival. The next night, April 1, a Seoul club listed him on Hammond organ in the drummer Kim Hak-in's band Jazz Thing, with Kim Hyun-il on saxophone and Park Yoon-woo on guitar. The club's biography of him lists the Seoul National University, Yongpyong, Jarasum and Seoul jazz festivals, television and radio spots on EBS Space Gonggam and KBS, arrangement and playing work on Nouveau Deux, on the fourth album of the singer Park Seon-ju, on the third and fourth albums of Woong San and on the 50th anniversary album of the singer Yoon Bok-hee, membership of the Lee Jung-sik Quartet and of Youn Sun Nah's band, and teaching at Hoseo University, the Dong-ah Institute of Media and Arts, Baekseok University, Pyeongtaek University and Hanseo University. His later biographies on Bugs and Genie add the Penang and Moscow jazz festivals, performances with the violist Richard Yongjae O'Neill, the gugak singer Ahn Sook-sun and the percussionist Kim Duk-soo, invitations to the United States, Japan, China, Vietnam and Russia, and lecturing at Yeungnam University, Daegu Arts University, the Seoul Institute of the Arts and Suwon Women's College.

In the 2013 Melon interview he said he would keep playing in organ trios, keep working in the Charlie Jung Blues Band, and was preparing an album with the vocalist Park Jae-hong (박재홍). That year he also played piano on Lee Dong-woo's Smile (November 2013), a record produced by Woong San.

The partnership with Charlie Jung shaped the rest of his recorded work. He is the organist on the Charlie Jung Band's digital single "Sangdo Blues" (July 2014) and on its album Sunshine Blue (December 2014), where his Hammond organ is central to the sound (see Charlie Jung). In 2018, a Yeoju cultural magazine reports, the two joined Jong Dae Oh to form Trio Works. The trio recorded Gunsan Gaka on August 15, 2019 at The Nora Stage Y, with three of its eight tracks taken live; Discogs credits Sung with organ and as the writer of "Moon Blues", and the album was released on October 2, 2019 through Sound Republica. When the nominees for the 17th Korean Music Awards were announced on January 22, 2020, Trio Works appeared in two categories, Best Jazz Album and Best Jazz and Crossover Performance. Kim Oki's Spirit Advance Unit won the first and Jangeun Bae and Liberation Amalgamation's JB Liberation Amalgamation won the second (see Kim Oki and Jangeun Bae). A 2021 notice for the trio's September 30 concert at the Gyeongnam Culture and Arts Center says that, since the album, they had played the Jarasum, Seoul Forest, Taehwagang and Daegu jazz festivals and the Kumamoto Jazz Festival in Japan. The Yeoju magazine reviewed their July 29, 2021 concert at the Empress Myeongseong birthplace hall, which opened with "Gunsan Gaka", played Gershwin's "Summertime" and the film song "Reality", closed with Sung's "Moon Blues" and added Procol Harum's "A Whiter Shade of Pale" as an encore.

In 2022 the album announcement for Woong San's Who Stole the Skies named Seong Gi-mun on organ among its players. On October 25, 2023 he was billed with Charlie Jung and the drummer Song Ha-yeon at the Ulju Culture and Arts Center in Ulsan.

His own name leads the 2024 releases and listings. 소곡집 첫 번째 (Sogokjip Cheot Beonjjae, "small songs, first"), credited to Park Jae-hong and Sung Gi-moon, came out in May 2024: ten children's and folk songs, among them "따오기", "반달", "섬집아기" and "과수원길" from the Korean repertoire and "Annie Laurie" (애니로리) and "Maggie's Memories" (매기의 추억) from the Western one. Park is credited for vocals and Sung for playing, though Bugs files the first track under Park and the other nine under Sung. The project was planned with the architect Yu Byeong-an, a long-time friend of both, as part of a Korean culture and arts undertaking. A June 13, 2024 concert video bills him on piano for it, and a recital of the album was listed for September 13, 2024 at the Dream Forest Art Center concert hall in Seoul. On November 28, 2024 a free concert in Paju was announced under the title "Sung Gi-moon Blues All Stars", with Sung on organ, Park Jae-hong on vocals, Kim Seon-yul on guitar and Lee Jung-min on bass.

His own account is plain: he loves blues and soul, and listeners compared his playing to that of Gene Harris, which earned him the nickname "Korea's Gene Harris", though he told Melon that he is really a fan of Oscar Peterson. He listed Keith Jarrett, Ray Charles, Oscar Peterson, James Taylor and the pianist Paik Kun-woo among his favorite musicians. He said the Hammond organ appeals to him because it can supply the bass line and has a rich sound, and that leading a trio puts the responsibility for the band on him, while in a quintet he plays with more restraint to support the lead instrument.

Discogs files Gunsan Gaka under jazz and blues with the styles swing and soul-jazz. The Gyeongnam Culture and Arts Center described the trio's sound as a rolling, plain and bluesy team sound, and the Yeoju magazine wrote of an organ that carries the soul of Black music, set against Charlie Jung's blues-rooted guitar and Jong Dae Oh's hard-hitting drums. Sung's "Moon Blues" is the piece on the album that the magazine singled out for the organ, and his 2024 duo record with Park Jae-hong turns Korean children's songs and Western folk tunes into voice and keyboard music.