Robert Lyle Knepper (born July 8, 1959) is an American actor. He has played Nicholas Lang in the 1988 Touchstone Pictures film D.O.A..

He is best known for his role as Theodore "T-Bag" Bagwell in the FOX drama series Prison Break from 2005 to 2009 and has also appeared in films such as Good Night, and Good Luck, Hitman, Jack Reacher: Never Go Back and Transporter 3. Knepper joined the cast of Heroes in 2009 for its final season as Samuel Sulliva, and he played Sid Rothman in the neo-noir television series Mob City in 2013.