Park Sung-yeon (박성연) was a South Korean jazz singer who opened Janus, the first jazz club in Korea founded by a Korean, in Seoul in 1978 and kept it open for nearly four decades. Korean newspapers called her the godmother of Korean jazz (재즈계의 대모) and the Korean Billie Holiday. She was born in 1943, according to Newsis and the Korean Wikipedia article, and passed away on August 23, 2020; no source gives her exact birth date or birthplace. Her own records print the name as Park Sung-Yeon, Discogs files her as Sung-Yeon Park, and the Revised Romanization of the Hangul is Park Seong-yeon.

Music was part of her home. In a retrospective drawn from her own interviews, she recalled a family that liked music, a father who loved music in particular, record players in the house and Glenn Miller and Benny Goodman records, and said a brother who worked at a store on a US military base gave her a radio tuned to the American Forces Korea Network. After graduating from Ewha Girls' High School in the mid-1960s she passed an audition for the US Eighth Army shows, the circuit where many Korean singers of her generation first worked, and then studied composition at Sookmyung Women's University. The booklet of her 2013 album reproduces a photograph from her first concert, in 1969.

Jazz had almost nowhere to be played in Korea at the time, and she said in a 2013 interview that she wanted only a place where she could sing freely without being let go. She sold what she owned, borrowed money and opened Janus in the Sinchon district of Seoul in 1978; Newsis says she put nearly all her property into it, and one retrospective gives the opening date as November 23, 1978. Musicians gathered there night after night to improvise, and visiting foreign players made it a regular stop. The club then moved with the money: to Daehangno in 1985, behind Ewha Womans University in 1996, Cheongdam-dong in 1997 and Seocho-dong in 2007. In the 2013 interview she said she had never moved by choice, called herself a person with debts and no house who nonetheless felt rich, and said she wanted Janus to be a place where the music could develop, not one that simply kept players on the payroll; younger singers such as Malo, she added, came and sang without taking the small fee she could not always pay.

The cost was real. She sold her mother's house to keep the club open, and in 2012 she auctioned the record collection she had built over a lifetime, about a thousand LPs by the figures given in two accounts. That same year she received a presidential citation at the Korean Popular Culture and Arts Awards, described as the first for a jazz musician. In November 2013 Janus marked its 35th anniversary with two nights at the Seocho club and 53 players, among them the first-generation figures Jung Sung-jo and Lee Dong-gi and younger singers including Malo and Woongsan. At the 11th Korean Music Awards, held on February 28, 2014, she received the contribution award, which was announced ahead of the nominees; she was still performing.

Her first album, 박성연과 Jazz At The Janus Vol. 1 (Jigu Records), appeared in 1985 and included her own song "물안개" (Water Mist), with her own words and music according to Korean press; it was reissued on CD in 1992. Discogs credits her with vocals on "All of Me" and "What a Wonderful World" on EAGON 7th Concert (Eagon, 1996), a live album by the Wendell Brunious Jazz Band. In 2010 she was among the first-generation musicians in Nam Mu-seong's documentary Bravo! Jazz Life, appearing on its soundtrack with "All of Me", "물안개" and "Antonio's Song" beside Shin Kwan-woong, Kim Soo-yeol and Lee Dong-gi, and in January 2011 she was billed to sing with the same band at the Seoul Arts Center concert that recreated it, with Malo announced as her duet partner. She also sings "All of Me" and joins the closing "All Jam" on the live CD marking the trumpeter Kang Dae-gwan's 70th birthday, a record that also gives Kim Jun a vocal feature.

In 2013 she made Park Sung-Yeon With Strings (Audioguy Records), a 13 track album with a 24-piece string orchestra arranged by Choi Hee-jung and a quartet of pianist Song Young-joo, bassist Choi Eun-chang and drummer Oh Jong-dae, which Tenasia reviewed as the work of a singer approaching seventy whose singing had matured with the years; it includes an unaccompanied "Danny Boy" and her own "물안개". Three years later she recorded Body & Soul (Audioguy, 2016) as a duo with the pianist Francesca Han, nine standards with her name first on the cover. In 2016 she also sang on three tracks of the pianist Im In-gun's Janus, The Reminiscence, a tribute to Janus and the first generation by a pianist who played at the club, which was nominated for Best Jazz & Crossover Album at the 14th Korean Music Awards in 2017, and the trumpeter Choi Sun-bae is among its other guests.

Kidney failure forced her to step back. She handed the running of Janus to Malo in 2015 and spent the rest of her life in a care hospital in Seoul's Eunpyeong district. She still sang when she could. On October 22, 2017 she appeared in a wheelchair at the 14th Jarasum International Jazz Festival in a "Divas" program with Malo, singing "I'm a Fool to Want You", which she called the song she had sung most in her jazz life, and "바람이 부네요". She left the hospital briefly to sing at the club's 40th anniversary in 2018. In March 2019 she recorded a duet version of "바람이 부네요" (The Wind Is Blowing) with the pop singer Park Hyo-shin, finishing it from a wheelchair as her illness worsened, and in September 2019 she appeared at the Seoul Forest Jazz Festival. She passed away on August 23, 2020, and burial was planned for the family cemetery in Paju.

Janus did not end with her. Malo, who renamed the club Diva Janus, kept it running, moved it to Apgujeong in 2023, and with the lyricist Lee Ju-yeop reopened it in Gwanghwamun on September 15, 2025. The documentary Diva Janus, about her and the club, opened in Korean cinemas on October 22, 2025.

She sang standards and ballads in a plain mainstream manner: "I'll Remember April", "It Don't Mean a Thing", "Body and Soul", "I'm a Fool to Want You" and "Sassy's Blues" on her first album; "Misty", "Stardust", "Angel Eyes" and "Good Morning Heartache" with strings; "Don't Explain" and "Easy Living" on Body & Soul, a program that leans on the ballad repertoire of Billie Holiday, the singer her nickname invoked. She also put the folk song "Milyang Arirang" into a ten-minute jazz arrangement on her first record and wrote at least one song of her own, "물안개". The Tenasia review heard a voice that had ripened with age and singled out the unaccompanied "Danny Boy" for the tremor and breath in it.

She came up listening: American radio and records as a girl, then the Eighth Army shows, and later, by her own account, live music wherever she travelled. In a 2013 GQ Korea interview she said she had seen Miles Davis twice and admired how deliberately he dressed, that she had asked Ron Carter whether she might touch his bass, that she once sent ginseng root to Dizzy Gillespie, who had diabetes, and that she heard three sets a night on trips to New York and sat in at a club in Naples. The same interview shows how she saw her role: she preferred to be called a jazz singer and not the club's owner, always wore a proper stage dress, and held that live playing, not recordings, is where jazz is actually heard.

Her standing in Korean jazz rests on Janus as much as on her records. The critic Hwang Deok-ho said in the documentary that without Janus Korean listeners might have stayed at the level of importing jazz from abroad. Part of her fame is as the proprietor of the club; she was nevertheless a working vocalist for more than fifty years, and the albums released under her name are jazz albums.