The younger brother of hip-hop producer Timbaland, Sebastian (born Garland Mosley) has been a part of a small pool of ghostwriters that Timbaland has relied on for his solo recordings since the early 1990s. In his adolescent years, Sebastian originally thought that his future would be in sports, but he was pulled more and more into rap music and writing rhymes because of his brother, who was just starting out as a DJ at the time.
After completing high school, he joined Timbaland and breakout R&B singer Ginuwine on tour, which is where he firmly decided that he would pursue music as a profession. The first lyrics he wrote for Timbaland were for the song “We at It Again” for the soundtrack of Romeo Must Die (2000), on which the rhyme-scripter also made a guest appearance. Throughout the next few years, he continued to make guest appearances on various Timbaland-produced songs, particularly for the Timbaland & Magoo combo. When Timbaland founded Mosley Music Group in 2006 after the demise of his Beat Club imprint, Sebastian signed to the label and found himself in the thick of Timbaland’s new wave of popular hits. He contributed to Timbaland’s 2007 outing Shock Value.