Alexander Harper Berkeley (born 1955) is an American actor. Since beginning his career in the early 1980s, he has appeared in over 200 film and television projects. His films include Terminator 2: Judgment Day (1991), Candyman (1992), Barb Wire (1996), Air Force One (1997), Gattaca (1997), and Shanghai Noon (2000). He also appeared in the crime dramas L.A. Takedown (1989) and its remake Heat (1995), although he played a different character in each film. On television, he headlined the Citytv psychological thriller The Booth at the End (2010–2012) and was a series regular on the Fox action drama 24 (2001–2003) and The CW action thriller Nikita (2010–2012). As a guest star, Berkeley portrayed Sheriff Thomas McAllister on the CBS drama The Mentalist (2008–2013) and Gregory on the AMC post-apocalyptic horror The Walking Dead (2016–2018).

Berkeley was born in Brooklyn and raised in New Jersey. He is of English and Scottish descent.^[1] He attended Hampshire College,^[2] and worked in theaters at the Five Colleges, including Smith, Mount Holyoke, Amherst and the University of Massachusetts. He worked in regional and repertory theaters in addition to Off-Broadway in New York City. A casting agent spotted Berkeley in a play written by Reynolds Price called Early Dark and encouraged him to move to Hollywood.^[3]

Berkeley began playing roles in 1981, with early appearances in M*A*S*H, Cagney & Lacey, Remington Steele, Miami Vice, Moonlighting, and The A-Team.^[4] His later television roles included The X-Files,^[4] CSI: Crime Scene Investigation, ER and Law & Order.

On screen, he has appeared in North Country,^[5] Terminator 2: Judgment Day, Mommie Dearest,^[5] Phoenix, Kick-Ass,^[5] A Few Good Men, The Rookie, Candyman, Apollo 13, Leaving Las Vegas, Gattaca, The Rock, Air Force One, Sid and Nancy,^[5] Amistad, Shanghai Noon,^[5] Barb Wire^[5] and Timecode. He appeared in the television film L.A. Takedown^[5] in 1989 and its 1995 acclaimed theatrical remake Heat,^[5] directed by Michael Mann. Several of his earlier roles were in films directed by Alex Cox.

In 2001, Berkeley became a recurring guest star (and later a series regular) on 24 in the role of George Mason, the head of the counter-terrorist unit.^[6] He portrayed the mysterious John Smith on the CBS drama Jericho.

In 2010, he received one of his best-known roles, Percy Rose on The CW action-thriller series Nikita.^[7] He portrayed the character as a series regular and de facto main antagonist of its first two seasons. He also played Sheriff Thomas McAllister on The Mentalist.^[8]

Berkeley portrayed Gregory on AMC's The Walking Dead as a guest star in season six and a series regular in season seven.^[9]

In 2018, he portrayed Peter Lockwood, the father of Sam Lockwood on the fourth season of Supergirl.^[10]

Berkeley is a make-up artist, painter,^[14] and sculptor.^[2] He met actress Sarah Clarke on the set of 24 in 2001 and married her the following year.^[2] The two live with their daughters in Maine and Los Angeles.