Gugudan (Hangul: 구구단), also stylized as gu9udan or gx9, is a South Korean girl group formed in 2016 by Jellyfish Entertainment. The group debuted on June 28, 2016, with their EP Act. 1 The Little Mermaid. The group composed of eight members: Mimi, Hana, Haebin, Nayoung, Sejeong, Sally, Soyee and Mina. Originally a nine-piece group, Hyeyeon later departed from the group on October 25, 2018.

In January 2016, Nayoung, Sejeong and Mina were introduced as Jellyfish Entertainment’s first female trainees on the Mnet survival show, Produce 101, where 101 female trainees from various companies competed to debut in an 11-member girl group that would promote for a year under YMC Entertainment. After placing 2nd and 9th respectively in the final episode, Sejeong and Mina debuted as members of I.O.I in May 2016.

Despite denying earlier reports of Sejeong and Mina debuting in a 3-member girl group in June, Jellyfish Entertainment confirmed on June 7 that the two I.O.I members would debut within the month in what would be the company’s first girl group. Because of YMC Entertainment’s special terms in which I.O.I’s members are allowed to do activities under their respective companies while I.O.I was on break or while the group promoted in sub-units, there were no complications with the plan.

Nayoung was also confirmed as a member on June 10 and on June 13, Jellyfish Entertainment revealed that Gugudan would be a nine-member group. On June 17, Jellyfish Entertainment announced the group name.

On June 22, the group confirmed that they were going for a “mermaid” concept. Following the announcement, a highlight medley of the group’s debut mini-album was released on June 24. They debuted on June 28, 2016 with the mini-album, Act. 1 The Little Mermaid, with “Wonderland” as the title song. Their debut showcase was held at the Yes24 Live Hall on the same day as the album’s release.

Gugudan participated in Jellyfish Entertainment’s annual winter project, Jelly Christmas 2016, with their label mates Seo In-guk, VIXX, Park Yoon-ha, Park Jung-ah, Kim Gyu-sun, Kim Ye-won and Jiyul. The title track, “Falling (니가 내려와)” was released digitally on December 13, 2016.

In early February 2017, Jellyfish Entertainment announced that Gugudan would make their first comeback since the debut with their second mini-album. The mini-album, Act. 2 Narcissus, and its title track, “A Girl Like Me”, was released on February 27.

On November 8, the group returned with a single album, Act. 3 Chococo Factory, featuring the title track, “Chococo”. Prior to the release, it was announced that Soyee will go on hiatus in order to fully recover from a shoulder injury that she had since prior to her debut.

On February 1, Gugudan released their second single album Act. 4 Cait Sith, with the lead single “The Boots”.

On May 17, it was announced that youngest member Hyeyeon will go on a temporary hiatus from all the group activities due to health issues.

Gugudan officially debuted in Japan with releasing their first Japanese single Stand By on September 19. On September 21, Gugudan held their debut showcase and fanmeeting titled Gugudan 1st Showcase ＆ Fanmeeting “Dear Friend” in Japan at Tokyo Akasaka Blitz. The group also scheduled to held their first Japan tour in Osaka and Tokyo starting on December 7, 2018.

On October 25, it was announced that Hyeyeon officially left the group to focus on her studies and recovery of her health. Though Hyeyeon has left Gugudan, she is still under Jellyfish Entertainment.

On November 6, Gugudan released their third EP, Act. 5 New Action, containing six tracks with the lead single “Not That Type”.

In July 2017, Jellyfish Entertainment formed the first subunit of Gugudan composed of two youngest members: Mina and Hyeyeon, named Gugudan 5959 (Hangul: 구구단 오구오구; spelled as “Ogu-ogu”).The “5959” name is made up of their represented numbers in Gugudan: Hyeyeon representing the number 5 and Mina representing the number 9. 5959 released their debut single, “Ice Chu”, on August 10, 2017.

After Hyeyeon’s departure in October 2018, the subunit consequently became inactive.

In June 2018, Jellyfish Entertainment formed the second subunit of Gugudan, composed of members Sejeong, Mina and Nayoung, named Gugudan SeMiNa (Hangul: 구구단 세미나). The “SeMiNa” name is made up of the first syllables of the members. Gugudan SeMiNa debuted with the release of their self-titled single album consisting of two tracks on July 10, 2018.

Source: wikipedia