History of Korean idols

Korean idol groups began to appear in the early 20th century. Its earliest examples came in the form of vocal groups that both sang and danced. The most notable early example is the Jeogori Sisters, who debuted in 1939.

1930–70: Early vocal groups
In the 1930s and the 1950s, the earliest mainstream Korean idols consisted of vocal groups that sang and performed at the same time. One of the first girl groups was the Jeogori Sisters, who debuted around 1939, while one of the first boy groups to debut was the Arirang Boys. The first idols to go abroad were The Kim Sisters, a three-member girl group that performed in the U.S. and South Korea from the 1950s to the 1970s. With the success of The Kim Sisters, a number of "sisters-type" girl bands started to rise in popularity, including the Silver Bell Sisters (1954), Hyun Sisters (mid-1950s), Jung Sisters (mid-1950s), Lee Sisters (1962), Lily Sisters (1969), Bunny Girls (1971), and National Treasure Sisters (1981). However, these groups differed from the concept of idol groups associated with the Korean Wave and K-pop.

1980–90: Dance singers
In the mid-to-late 1980s, independent music that was founded in the newly introduced genres of disco, soul, and funk began to rise in popularity. The debuts of Sobangcha and Setorae in the 1980s is now considered to be the beginning of the current trend in boy and girl groups respectively. Korean dance singers and groups held performances based on Western dance music which combined exciting music and fancy dances, with the most prominent representatives of the movement being Sobangcha, Setorae, Kim Wan-sun, and Nami.

In the early 1990s, songs started to combine repeated rhythms of electronic dance music such as house, techno, and trance with a melody that gives a trot-like feeling. In addition, simple rap due to the influence of American hip hop was especially popular among teenagers. This musical composition is called "new generation dance music" and has been adopted by current idol music. These younger generations were exposed to new musical influences as they began to find and listen to foreign music that had not yet been introduced to Korea.

1990: First-generation idols
Founded in 1989, SM Entertainment selected Hyun Jin-young, who was well known as a "dancer," to debut as its first singer. However, in 1993, the company suffered financial difficulties when Hyun was discovered to be taking methamphetamine. As such it attempted to establish a new training system for singers in which teenagers were selected through auditions to practice singing and dancing before eventually debuting as singers. The company then recouped the capital they invested during their debuts through record sales and performance activities. H.O.T. was the first group under this system to be presented by SM Entertainment.

The first-generation idol groups are usually groups of approximately five people, each of whom divided their roles into lead vocal, sub-vocal, dancer, and rapper. While singing on stage, their synchronous choreography, known as "group dance," was more sophisticated compared to previous dance music, but at the same time included "point choreography" that teenagers could easily imitate. Musical performances were done only for two or three songs in the album—the title song and follow-up song—and these songs were produced with music videos that showed each member's characteristics. After several months of performing, the singers took a break and resumed their career with their next album. This system became the basis for the second and third-generation idols.

The first-generation idol groups were mostly formed by SM Entertainment, which had a focus on mysterious images, and DSP Media, which had a focus on realistic images. The two were known to have a rivalry with each other. Boy groups such as SM's H.O.T. and DSP's Sechs Kies arose, both of which made their debuts with songs about social criticism and became popular for their rhythmical dance music. SHINHWA maintained the group's identity with its masculine visual appeal and strong audience reception, while g.o.d built a friendly image by appearing on entertainment shows and producing songs that many generations could relate to. Meanwhile, girl groups such as SM's S.E.S. and DSP's Fin.K.L. maintained a cute and pure girl image for the band. Later, S.E.S displayed an unrealistic and mysterious image, and Fin.K.L displayed a friendly image for the band members. Baby V.O.X and DIVA had become popular for their strong female image as well.

First-generation idols lost popularity in the 2000s. They often lip-synced as they performed with a focus on choreography, and most of the audience recognised that the songs heavily relied on digital techniques to correct the vocals of the idol singers. As a result, many people began to question the authenticity and competency of the singers. In addition, a series of controversies had erupted in contracts with idol members and adjustment of profits, and the idol-training system relied on terrestrial broadcasting while the music market was being converted into digital centres. Eventually, idol groups were disbanded, such as Sechs Kies in 2000, H.O.T. in 2001, S.E.S. in 2002, and Fin.K.L declaring a halt to team activities in 2002.

2000: Second-generation idols
With the decline of the first-generation idols in the early 2000s, solo singers from big agencies, such as BoA, Rain and Seven, became popular alongside solo singers who were formerly part of a group, such as Kangta, Moon Hee-joon, Bada, Ock Joo-hyun, and Lee Hyori. TVXQ made its debut as an acappella group in 2004, and was followed by SS501 and Super Junior in 2005 and Big Bang in 2006, but were not as trendy as first-generation idols. The rise of second-generation idols can be attributed to the 2007 release of Wonder Girls’ "Tell Me", which became so popular that it was named a "syndrome." TVXQ, SS501, Super Junior and BigBang, all of which debuted earlier, subsequently joined the popularity triggered by Wonder Girls.

The second-generation idol groups usually consisted of six or more members, formed a "group in a group" called a unit, and ran group and unit activities at the same time. The agencies tried to manage their idol groups more thoroughly than the first generation to prevent problems. They regularly evaluated trainees' singing and dancing abilities and ended contracts with trainees if their abilities did not improve or were significantly inferior. They also put an emphasis on personality and dismissed trainees whose behaviour was controversial.

The music released during this period consisted mainly of hook songs in which a short chorus was repeatedly presented, and most songs were deliberately composed similar to Western pop music to target foreign market listeners. Since the digitisation of the music market required frequent releases of albums and continuous exposure to the public to maximise profits as an agency, singles and extended plays with fewer tracks than regular albums became common. Unlike first-generation idols, second-generation idols appeared on entertainment shows and established "friendly images outside the stage" that were different from their "image on stage". Second-generation idols also extended their demographic to middle-aged people, and as a result introduced the term "Samchon Fan", which referred to male fans in their 30s and 40s. Female fans of girl groups, called "Yeodeok", were also established.

The rivalry present in the first-generation idols was not as frequent among second-generation idols as concepts and music genres diversified. Wonder Girls and Girls' Generation, who debuted in 2007, gained popularity together and were perceived to be rivals, but as more idol groups made their debuts there were fewer instances of them being dubbed rivals. Wonder Girls, Kara, and Girls' Generation pursued an appealing image and were heavily influenced by the groups in the previous generation, with Kara resembling Fin.K.L. while Girls' Generation resembled S.E.S. Brown Eyed Girls became popular with both men and women for their own musical characteristics, while 4minute, 2NE1, f(x), and Miss A took on the independent female image of Baby V.O.X and DIVA. SISTAR, Girl's Day and AOA pursued a sex theme, while Apink pursued a theme of innocence. TVXQ and BigBang were considered different from traditional idols as they created music that showed originality and maturity, and TVXQ in particular drew attention by releasing different albums from country to country. SS501 and Super Junior became popular because they introduced the concept of idol groups appearing on entertainment shows. SHINee built a pretty-boy image, and 2PM built a masculine image called "Jim Seung-dol". FT Island and CNBLUE were band-type idol groups.

2011: Third-generation idols
Idols that debuted in the 2010s are known as third-generation idols. EXO is considered to be the starting point for the third generation, particularly for boy groups. On the other hand, many girl groups disbanded after the Korea Fair Trade Commission stipulated in 2009 that exclusive contracts between agencies and celebrities could only last a maximum duration of seven years; as such, girl groups are classified as third-generation if they debuted after 2014. Some second-generation girl groups were categorized as "Generation 2.5" if they debuted in the transitional period between Generations 2 and 3, which includes groups that debuted from 2011 to 2012.

The idol groups' marketing strategy had become more diverse due to social media, which has led to the emergence of unprocessed, self-produced content on sites such as YouTube, AfreecaTV, and V App rather than through TV programs. Idol members also began to post on social networking services to get closer to their fans. In terms of planning, the "localisation" strategy expanded not only through releasing albums in different countries or performing in different languages but by including foreign, non-Korean members directly into groups. Idol groups such as I.O.I and Wanna One were selected and debuted on popular singing competition programs akin to American Idol. Since the mid-2010s, there have been more cases of second and third generation idols using group activity breaks to release records as solo singers and deviate from their groups' characteristics.

The concepts of third-generation idol groups have also evolved to be more nuanced as the number of girl groups targeting female audiences increased. In addition to their singing ability, MAMAMOO, for example, attempted to utilise male attire in the title track of Pink Funky, which in turn gained them the "girl crush" image and was well received by their target audience. Lovelyz chose their concept to be "girls seen from a girl's gaze." GFriend took on a concept reminiscent of "healthy youth" and bore the innocent image of S.E.S., Fin.K.L, and Girls’ Generation.