Prior to his involvement with YG Entertainment, Seung-hyun was an underground rapper under the name of Tempo, and a childhood friend of G-Dragon, another member and leader of Big Bang.[4] G-Dragon stated that the two were "neighborhood friend[s] from middle school" and would often dance and rap together.[5] Although G-Dragon later moved away and the two "became distant", he contacted Seunghyun again when YG Entertainment was scouting for candidates to create a boy band.[5] The pair recorded several demos and sent them to Yang Hyun Suk, CEO of YG Entertainment, who later asked Seunghyun to audition.[4] Seunghyun was initially rejected by the record label, which deemed him too "chubby" to fit the "idealistic version" of an idol.[4] Seunghyun later stated that he "went home and exercised really hard because I wanted to join YG Entertainment."[4] Six months later, he returned for another audition and was signed on. He reportedly lost 20 kg in 40 days.[4]
Choi Seung-hyun was given the stage name of T.O.P. (Korean: 탑) by fellow YG artist Se7en. He became one of the two rappers in the group Big Bang, alongside G-Dragon. The two were paired with four others: Taeyang, Daesung, Seungri and So-1 and a documentation of their training was aired to promote them.[6] So-1 was dropped by the record label, and Big Bang made its official debut with five members.[7] Their first album, Since 2007, was a fair success,[8] and included T.O.P.'s first solo song "Big Boy." The group achieved mainstream success with the release of the song "Lies" (Korean: 거짓말; Revised Romanization: Geojitmal) from their 2007 mini-album Always, which topped several charts upon its release. The singles, "Last Farewell" (Korean: 마지막 인사; Revised Romanization: Majimak Insa) from the mini-album Hot Issue and "Day by Day" (Korean: 하루하루; Revised Romanization: Haru Haru) from Stand Up, became chart-toppers as wel