Malik B. left the group in 1999 due to personal reasons but continued to record, making occasional cameos on some albums. Guitarist Ben Kenney had a brief stint with the group and contributed to the "Phrenology" album, but left to join Incubus as bassist. Percussionist Frank Knuckles joined the lineup in 2002 and guitarist Kirk "Captain Kirk" Douglas replaced Kenney. Vocalist Martin Luther toured with the Roots in 2003 and 2004 and contributed to the "Tipping Point" album. The group announced in August 2007 that its longtime bassist Leonard Hubbard was leaving. Owen Biddle was the band's bassist in 2007–2011.