Lance Reddick portrays Matthew Abaddon starting in Season 4.
Biography
He attended the Eastman School of Music, and Yale University. After trying to be a singer, he gave up and was accepted in to the acting branch of Yale.
After graduation, he became an actor, guest starring in two episodes of Law & Order. He then became famous for appearing as Cedric Daniels in the HBO series The Wire. He also appeared in Oz along with Lost actors Harold Perrineau and Adewale Akinnuoye-Agbaje.
He has been cast in J.J. Abrams' new series pilot, Fringe, although Abrams has stated that he would still be available to shoot for Lost whenever necessary.