Heo Young Saeng(born November 3, 1986) was a trainee under SM Entertainment, making him close with members of TVXQ and Super Junior. He later joined DSP Entertainment and debut as a member of SS501 on 8 June 2005.
Young Saeng hosted SS501's Youngstreet (SBS, 2006) with fellow member Park JungMin from 1 May 2006. He had to part with the program in Aug'06 due to some problems on his vocal cords which requires surgery and time to recover.
In 2008, due to 2 members' busy schedules, Jung Min performing in a Korean production of the musical "Grease" and Hyun Joong filming drama "Boys Over Flowers", SS501's album which was originally due for release in late 2008, was to be pushed back to July 2009.
Instead, a sub unit of SS501 was formed, with Heo Young Saeng as the leader of this sub unit. Other two members in this unit are Kim Kyu Jong and Kim Hyung Joon. This unit group was initially named "Triple S" but they changed it back to "SS501", reason being that they are 5 members always as 1. The unit group released a special project album "U R Man" (released on November 25, 2008).
Young Saeng composed and wrote his solo song, '사랑인거죠 (Is it Love?)' which is also included in the special project album. This song is written while SS501 were having activities in Japan in 2007. He is the first member to have both composed and wrote lyrics for a song.
Finishing their promotional activities for "U R Man", they continued their activities to promote "내 머리가 나빠서 (Because I am stupid)", a song they sang for the OST of "Boys Before Flowers". This song is very well-received due to the success of the drama. They won the "Song of the month (Feb)" award with this song at the 32nd Cyworld Digital Music Awards (28 Mar 09) with about 110,000 downloads for BGM at www.cyworld.com
Information from: wikipedia