SS501 (pronounced as Double-S Five-Oh-One or Deo Beul E Seu Oh Gong Il ( in Korean) is a popular South Korean boy band formed under the management of Daesung Entertainment, also known as DSP Entertainment. All the members of the group have subsequently left DSP Entertainment to different management companies, but they still intend to stay together as SS501. The name of the band is a combination of letters and numbers that have special meaning. The first “S” stands for “Superstar". The second “S” is an abbreviation for "Singer". The combination of 5, 0, and 1 symbolizes "five members united as one forever".

SS501 debuted on June 8, 2005 with their first single "Kyeonggo" (Korean: "경고", "Warning"), with a second single "Snow Prince" released in late 2005. The group was inactive in Korea for most of 2006, although they had a fan meeting in Japan in April of that year.[2] The reason was due to Heo Young Saeng's throat condition which required a surgery, thus resulting in a need for time to fully recover.[3] In mid-2006, they held their first successful concert, "Step Up Concert" in Osaka, Japan. In late 2006, they returned to Korea in order to promote their first full album, which was released on November 10 and titled S.T.01 Now. Singles from the album included "Unlock" and "Four Chance". As well as promoting the album on various variety and music shows, they also filmed a show on MNet called SOS. The group (except Heo Young Saeng, who was recovering from the sugery) also lent their voices for the 2006 animated movie Pi's Story.

Later in 2007, the group debuted in the Japanese market. A Japanese fan club has been established with the name of "Triple S Japan"; it officially debuted on March 25, 2007, when SS501 had their first official meeting with the group. The group released their Japanese single "Kokoro", alongside multiple versions, including one with all members and five others featuring the members individually. The single debuted at #5 on the Oricon chart, and move to #3 the next day. A full album was released later that year.

In 2008, SS501 returned to Korea with their single Deja Vu released on March 8, 2008. The title track was the first song to be promoted, and they began their comeback on music channel M.Net's M Countdown.[5] After success with their single "Deja Vu", they began to promote their second single, "A Song Calling for You". They performed their Goodbye Stage on Music Bank on June 6, 2008, to return to Japanese activities.

On October 2, 2008, an official announcement confirmed that leader Kim Hyun Joong was part of the cast for the Korean version of Hana Yori Dango, officially named Boys Over Flowers. It was broadcast on KBS in the first half of 2009, with a total of 25 episodes and a few special episodes.

With both Park Jung Min (Danny Park on the musical Grease) and Kim Hyun Joong on solo activities, the next SS501 album was pushed back to July 2009. As such, the other three members formed a subunit with Heo Young Saeng as the leader and released a project album named U R Man in November 2008. The first single released was "U R Man". They also promoted their single for the Boys Over Flowers soundtrack, "Nae Meoriga Nabbaseo" (Korean: "Because I'm Stupid"). Due to the success of the drama, the song had a high number of downloads.
 
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