Born in Dundee, Scotland on June 1, 1946, Cox was the youngest of five. Following his father's untimely death (when Cox was nine) and his mother's subsequent mental breakdowns, he was raised primarily by his older sisters and an aunt. In school, Cox developed a reputation as the class clown but he was troubled and barely achieving passing grades. When he discovered the Dundee Repertory Theatre when he was 14, things improved dramatically. ("I knew I belonged there from day one," the actor has said.) Making his debut in "Dover Road", Cox spent the next several years honing his craft. After attending LAMDA, he went on further his training in the British repertory system, eventually making his London stage debut in the 1967 Birmingham Repertory Theatre production of "As You Like It.”

Cox segued to feature films as Trotsky in 1971's historical epic "Nicholas and Alexandra,” but he only had one additional movie role over the next decade and a half. In 1975, he preserved his well-received stage role as a miner's son in the film adaptation of "In Celebration" helmed by Lindsay Anderson. Instead, Cox concentrated on his burgeoning stage career, amassing credits in classical roles like Brutus in "Julius Caesar" (1977), and the title roles in "Macbeth" (1980) and "Danton's Death" (1982).

Cox co-starred with Glenda Jackson and Edward Petherbridge in the revisionist staging of Eugene O'Neill's "Strange Interlude" in 1984, making his Broadway debut the following year reprising his part as the doctor who helps the heroine to have a child. His success in this part led to roles in American-produced TV-movies like "Pope John Paul" (CBS, 1984) and "Beryl Markham: A Shadow on the Sun" (CBS, 1988), as well as reviving his film career (beginning with Lektor in 1986's "Manhunter").

Returning to London, Cox garnered some of the best reviews of his career to that date playing Shakespeare's "Titus Andronicus" (1988), for which he also earned numerous accolades, including an Olivier Award. He went on to deliver a complex, layered portrayal of a closeted homosexual struggling with the discovery that his son is also gay in the 1991 British TV-movie "The Lost Language of Cranes". That same year, Cox was also fine as a wealthy eccentric who has had his former wife duplicated in a laboratory in "The Cloning of Joanna May" for Granada Television. He subsequently portrayed the Irish mentor of a British rifleman in the first two installments of "Sharpe" (1993), which aired in the USA on PBS' "Masterpiece Theater.”

Cox was featured in the Oscar-winning "Braveheart" (1995) and that same year also had a pivotal role in another historical epic "Rob Roy", playing a snitch whose information leads to the death of a kinsman of the title character. He continued to rack up supporting parts in such unworthy efforts as "The Long Kiss Goodnight" and "The Glimmer Man" (both 1996) before landing the strong role of an IRA leader in "The Boxer" (1997). Returning to the stage, he triumphed in Conor McPherson's one-man drama "St Nicholas" (1997) before succeeding Alan Alda in the Tony-winning play "Art" (in 1998), Cox was delightful as the stern headmaster of "Rushmore" (1998) and was touching as a self-destructive alcoholic who unwittingly befriends a serial killer in "The Minus Man" (1999). After playing Mark Wahlberg's Irish cop father in "The Corrupter" (also 1999), the actor portrayed a baseball team owner looking to sell his flagging franchise in the Kevin Costner vehicle "For Love of the Game" (2000). Additionally, he shone as Lord Morton in the acclaimed TV drama "Longitude" (A&E, 2000) and elevated the mediocre serial killer drama "Complicity" (also 2000). But perhaps his best performance of that year was his Emmy-winning turn as Nazi Hermann Goering in the TNT original "Nuremberg.”

Cox kicked off the new millennium with a spate of feature roles including two screened at the 2001 Sundance Film Festival, the drama "L.I.E." (in which he portrayed a pedophile) and the comedy "SuperTroopers." Additionally, he had supporting roles in the sports-themed "A Shot at Glory", the gangster drama "Strictly Sinatra", the period drama "The Affair of the Necklace" and the spy thriller "The Bourne Identity", ensuring that audiences would be enjoying his screen presence throughout 2001. His momentum continued in 2002, where he appeared in several well-received films including the smaller British drama "The Reckoning" and as a CIA chief attempting to cover his tracks in the popular Matt Damon spy thriller "The Bourne Identity" based on the best-selling Robert Ludlum novel--a role Cox reprised in the 2004 sequel "The Bourne Supremacy." The actor also received critical raves and an Emmy nomination for his guest role as the besotted father of Daphne Moon (Jane Leeves) on the hit series "Frasier." His feature film efforts continued to show diversity, with Cox appearing in the family-friendly baseball film "The Rookie," the horrific thriller "The Ring" and Spike Lee's character drama "The 25th Hour." He also lensed what may be his most visible and commercial role yet, playing the X-Men's villainous anti-mutant adversary Stryker in director Bryan Singer's big-budget sequel "X2: X-Men United" (2003).

Cox took on the historic role of King Agamemnon in "Troy" (2004), Wolfgang Petersen's epic, action-oriented adaptation of Homer's tale of the Trojan War, delivering a rare scenery-chewing performance that nevertheless enlivened the often turgid film. He cut a more subdued figure in his brief supporting role in the Wes Craven-directed thriller "Red Eye" (2005), playing the father of a terrorized but resourceful hotel employee (Rachel McAdams), his life unknowingly on the line as she's menaced by a mysterious stranger during a red-eye flight. In “The Ringer” (2005), Cox played the smarmy uncle of a nice guy (Johnny Knoxville) who convinces his nephew to participate in the Special Olympics as a ringer in order to raise money for a man hospitalized after a lawn care accident. He then appeared in Woody Allen’s return to form, “Match Point” (2005), playing the rich, but charitable father-in-law of an ex-tennis pro (Jonathan Rhys-Meyers) who embarks upon a passionate and ultimately complicated love affair with a struggling American actress (Scarlett Johansson). Atypically reserved in his performance, Cox was overshadowed by costars Meyers, Johansson and Emily Mortimer, as well as Allen’s surprisingly deft direction.

For his next project, Cox was set to appear as an unorthodox psychiatrist who cares for the bipolar mother of a young boy (Joseph Cross) in the adaptation of Augusten Burrough’s best-selling memoir, “Running With Scissors” (2006). In mid-2005, it was announced that Cox would join the cast of HBO’s award-winning revisionist western, “Deadwood” (2004- ), playing the real-life Jack Langrishe, an eccentric theater owner who tries to bring art and culture to the lawless town. Though an exuberant presence in the violent western town—his exchanges with old pal Al Swearengen (Ian McShane) were a high point of the underrated third season—it was not meant to last, as “Deadwood” was unceremoniously axed from HBO’s schedule.

Returning to the big screen, Cox costarred in “Zodiac” (2007), David Fincher’s take on the famed Zodiac Killer, who was credited with five grisly murders in the Bay Area during the late-1960s. An elusive killer who reveled in taunting the media and police, The Zodiac’s identity was never discovered, while several other similar murderers were loosely—but not officially—attributed to him. Cox portrayed Melvin Belli, the famed personal injury lawyer who became involved in the case when the killer supposedly called him while the lawyer was on live television, only to learn it was a hoax from a patient in a mental institution. The killer did, however, send the lawyer a Christmas postcard later in the year.