Xander R. Berkeley (born December 16, 1958) is an American actor. Berkeley began playing minor roles in 1981, with early appearances in M*A*S*H, Cagney & Lacey, Remington Steele, Miami Vice, Moonlighting and The A-Team. Although not becoming a household name, Berkeley's face was increasingly recognizable into the 1990s. His later television guest roles included The X-Files, CSI, ER, 24 and Law & Order.

On the big screen, Berkeley has appeared in North Country, Terminator 2: Judgment Day, A Few Good Men, Candyman, Apollo 13, Leaving Las Vegas, Gattaca, The Rock (uncredited), Air Force One, Sid and Nancy, Spawn, Amistad, Shanghai Noon, and Timecode. Berkeley has the distinction of appearing in both the made-for-TV movie L.A. Takedown in 1989 and its bigger-budget 1995 theatrical remake Heat, both directed by Michael Mann. Several of his earlier roles were in films by director Alex Cox. Most of his roles have been unsympathetic characters.

In 2001, Berkeley became a recurring guest star on 24 as George Mason, the head of the Counter Terrorist Unit. His character, initially presumed evil by other characters and the fans, was revealed to be one of the good guys and became a main character in season 2, only to meet an untimely (but heroic) end. However, the show did give Berkeley the chance to meet his future wife, Sarah Clarke, who played turncoat agent and villainess Nina Myers for the first three seasons of the show. On September 23, 2006, she gave birth to their first daughter, Olwyn Harper Berkeley.

Berkeley has also provided voices for animated series such as Aaahh!!! Real Monsters and Gargoyles. Berkeley was born in Brooklyn, New York. He graduated from Hampshire College.

Berkeley is a painter and a sculptor, as well as a skilled make-up artist who designed his own make-up on 24 when his character was suffering from the deteriorating effects of radiation sickness. Both he and his wife have played turncoat federal agents: he played a traitorous Secret Service agent in Air Force One, and she played the CTU mole Nina Myers in 24.