Born Terrence Quinn in Newberry, MI on July 15, 1952 – he changed his surname to avoid confusion with model and fireman-turned-actor Terry Quinn – he developed an interest in acting while in high school. After attending Central Michigan University in Mt. Pleasant, MI and the University of Iowa, O’Quinn began pursuing work as an actor on stage in regional and national theater. While appearing in a play in Baltimore, MD, he landed a supporting role as an Army captain in Michael Cimino’s revisionist Western, “Heaven’s Gate” (1980) and contacted a local trainer named Lori for riding lessons. While waiting for his scenes to be shot, O’Quinn’s play closed, and he found a job cleaning out Lori’s stalls. Over time, the working relationship blossomed into romance, and the couple was married in 1979, shortly before he departed to shoot “Heaven’s Gate.” Unlike many participants in that film, his career survived the onslaught of negative press that followed its release. The couple also produced two sons; Oliver (born in 1980) and Hunter (born 1982).

O’Quinn busied himself with roles on stage (opposite Faye Dunaway in Sam Shepard’s “Curse of the Starving Class”) and on television and in film throughout the 1980s. He logged a year on the daytime soap “The Doctors” (NBC, 1963-1982) and landed appearances in several notable productions, including Robert Benton’s “Places in the Heart” (1984) as a farmer with Ku Klux Klan connections; and a doctor in the AIDS drama “An Early Frost” (1986). His ability to project a sense of authority made him a natural choice for sheriffs and detectives, in such films as “Stephen King’s Silver Bullet,” (1985) and “Mrs. Soffel” (1984), as well as military officers and government officials in such feature fare as “Women of Valour” (1986) and “SpaceCamp” (1986).

The following year, O’Quinn caught the attention of critics and audiences alike as Jerry Blake, a homicidal maniac who marries into seemingly normal families and slaughters those who do not meet with his strict beliefs, in Joseph Ruben’s underrated thriller “The Stepfather” (1987). O’Quinn received universally excellent notices and an Independent Spirit Award nomination for his chilling portrayal of a cold-blooded killer who lurks behind a mild-mannered facade. The picture gave his career a decent-sized boost. He co-starred in Bob Rafelson’s excellent suspense film “Black Widow” (1987) as detective Debra Winger’s boss, and as the lawyer who hires Emilio Estevez’s posse of twenty-something gunfighters to bring down the heel (Jack Palance) who killed their mentor (Terence Stamp) in “Young Guns” (1988). O’Quinn also appeared in TV movies like “Roe vs. Wade” (NBC, 1989) and “Guts and Glory: The Rise and Fall of Oliver North” (CBS, 1989), starring as North’s fictional superior, Aaron Sykes. He also found time for such lower-budgeted efforts as the disturbing horror film “Pin” (1988) and the inevitable and far inferior “Stepfather” sequel, “Stepfather 2: Make Room for Daddy” (1989).

O’Quinn’s appearances in the 1990s seemed relegated to TV movies of varying quality such as “Son of the Morning Star” (ABC, 1991) as General George Custer’s superior, the real-life General Alfred Terry. However, he did score a few feature highlights, including "Tombstone” (1993) as the mayor of Tombstone, AZ; as a judge in “Ghosts of Mississippi” (1996); and, in a reunion with “Roe vs. Wade” director Gregory Hoblit, the small role of Yancy in the twist-filled Richard Gere thriller, “Primal Fear” (1999).

By the mid-1990s, O’Quinn was also making regular appearances on episodic television series like “Star Trek: The Next Generation” (syndicated, 1987-1994) and “Homicide: Life on the Street” (NBC, 1993-99), and he made recurring appearances on “Earth 2” (NBC, 1994) and “JAG” (CBS, 1995-2005). Writer-producer “X-Files” (Fox, 1993-2002) creator Chris Carter took a liking to O’Quinn and cast him in different roles for two separate episodes of his paranormal hit series, as well as the 2003 feature film “X-Files: Fight the Future” as an agent with connections to the series’ mysterious government agency “The Syndicate.” Carter later cast him in “Harsh Realm” (Fox, 1999-2000) as Omar Santiago, a rogue military officer who uses a virtual reality training program to exert dictatorial control over the real world. The show lasted just nine episodes, but Carter’s loyalty to O’Quinn carried him to their next joint effort, “Millennium” (Fox, 1996-99), as FBI profiler Lance Henriksen’s former partner (and eventual antagonist).

Thing suddenly turned a corner when, in 2002, O’Quinn guest-starred in several episodes of producer J.J. Abrams’ espionage-action series “Alias,” starring as hard-nosed FBI Assistant Director Kendall, whose true position within the government provided many answers for Sydney Bristow (Jennifer Garner) during the two years that occurred between the series’ first and second seasons. He also made several appearances as the Chairman of the Joint Chief of Staff – replacing John Amos’ well-liked Admiral Fitzwallace – on the fifth season of “The West Wing” (NBC, 1999-2006) and made an uncredited appearance as Luke Wilson’s boss in the hit comedy “Old School.” But despite the regular work, O’Quinn mentioned in an interview that this period was a difficult one for him. A call from the ever loyal Abrams to co-star (without audition) in his new drama was a welcome one.

That series turned out to be “Lost” – one of the biggest pop culture hits of the mid-2000s, and the show that gave O’Quinn the most exposure and meatiest role of his career. O’Quinn played John Locke, a troubled, middle-aged failure whose fears and sense of blind trust have left him the victim of a con artist who posed as his father and stolen his kidney and left him crippled. Once on the show’s mysterious island, Locke found himself not only able to walk again, but with a unique connection to the territory’s mysteries, which came to a head in the second season with the discovery of a foreboding hatch, complete with a computer that required constant re-setting – or would result in the destruction of civilization. Locke also formed a bond with the island’s sinister inhabitants known as the “Others;” by the end of Season Three, it appeared that Locke would abandon his fellow castaways and join their ranks, only to leave them behind and return to his friends with dire warnings. Though O’Quinn occasionally found the character’s behavior confusing and even off-putting, his performance was among the show’s many highlights, and in 2007, it earned him an Emmy for Outstanding Supporting Actor in a Drama – he had been previously nominated for the role in 2005. O’Quinn also took home a Saturn Award and a Screen Actors Guild Award – along with his castmates – for his turn as the complicated Locke.