Born on Oct. 20, 1958 to a Danish father and American mother, Mortensen was raised in both Manhattan and South America, where he learned to speak fluent Spanish and Danish as well as English. The multi-talented Mortensen trained for two years as an actor at Warren Robertson's Theatre Workshop in New York. Soon after moving to Los Angeles, he landed the role of the captain in a stage production of "Bent," then had a small role as an anonymous lieutenant in the CBS miniseries "George Washington" (1984). Although the actor had been cast in small roles in both "Swing Shift" (1984) and "The Purple Rose of Cairo" (1985), both performances wound up on the cutting room floor. Mortensen finally made his feature acting debut as an Amish farmer – and younger brother to Alexander Godunov – in "Witness" (1985), a role for which he was so well-cast that some failed to realize he was acting. Mortensen delivered a strong turn as a rebellious inmate in Renny Harlin's "Prison" (1988), then was effective as a returning soldier in "The Reflecting Skin" (1991).
Making his way up the Hollywood food chain, Mortensen was cast by Sean Penn as a veteran with a violent streak in "The Indian Runner" (1991), while Brian De Palma gave him the part of a wheelchair-bound snitch in "Carlito's Way" (1993). Mortensen also worked in less remarkable genre fare like "Leatherface: The Texas Chainsaw Massacre III" (1990) and "American Yakuza" (1995) before director Tony Scott came to the rescue, hiring him to play a concerned, but conflicted weapons officer in "Crimson Tide" (1995). After a turn as the Devil who battles Christopher Walken's angel Gabriel in "The Prophecy" (1995), the actor began to be considered for meatier roles. He displayed a sexy charm as one of Nicole Kidman's loyal suitors in "The Portrait of a Lady" (1996) and received respectful notices as one of the hostages in "Albino Alligator" (1997). With his breakout performance as the poetry-quoting but brutal taskmaster training recruits in "G.I. Jane" (1997), Mortensen finally began to gain audience recognition and many critics felt he stole the film from his better-known co-star Demi Moore. Gaining a reputation for his intense, magnetic portrayals, the actor was cast as the artist-lover of Gwyneth Paltrow in "A Perfect Murder" (1998) – for which he lent his own paintings – before tackling the role of Sam Loomis, Marion Crane's boyfriend, in Gus Van Sant's ill-advised shot-by-shot remake of "Psycho” (1998).
In a turn in the 1969-set drama "A Walk on the Moon" (1999), Mortensen was again cast as the "other man," this time playing a hippie traveling salesman who brings excitement into the life of a frustrated housewife (Diane Lane) – a role that would leave audiences and Hollywood execs buzzing about his potential as the next big thing. The following year he came between Sandra Bullock's recovering alcoholic and her partying boyfriend Jasper (Dominic West) as a star baseball pitcher in rehab for his substance abusing, womanizing ways in “28 Days.” Although this spate of films put him at risk for being typecast as a shameless homewrecker, Mortensen managed to forever remove that stigma with his next series of projects. He was tagged to co-star in Peter Jackson's long-awaited film adaptation of "The Lord of the Rings" trilogy, playing the heroic Aragorn. Mortensen's dashing good looks and commanding presence would serve him well in this leadership role, and helped bring in some moviegoers – including a considerable female fan base – who may have otherwise passed on the film. With the hype surrounding the initial 2001 release "The Fellowship of the Ring" – followed by 2002's "The Two Towers" and 2003's "The Return of the King" – Mortensen was established as a major leading man among Hollywood's A-list ranks.
The actor put his star status to the test immediately after the trilogy as the main attraction of the old fashioned but entertaining "Hidalgo" (2004), the true story of real-life horseman Frank T. Hopkins, who participates in a 3,000-mile Arabian race on the titular mustang. Mortensen then delivered his most compelling and carefully drawn performance to date when he starred in director David Cronenberg's tautly crafted drama "A History of Violence" (2005), playing a loving, rock-solid small town husband and father who gains notoriety after skillfully foiling a robbery attempt in his diner, only to draw the attention of some shadowy figures who claim to recognize him from his heretofore unknown violent history. The actor's sensitive and convincing portrayal of a man haunted by his secret past marked this as one of the early contenders in that year's awards derby.
Mortensen flew under the radar with his next project, “Alatriste” (2006), a swashbuckling adventure that saw him play a Spanish soldier-turned-mercenary who becomes a hero during the country’s 17th century imperial wars. Back in the modern world, he portrayed a slick Russian mobster who gets caught between helping a midwife (Naomi Watts) trying to find a prostitute’s killer and the crime family he serves in David Cronenberg’s thriller, “Eastern Promises” (2007). Mortensen’s strong performance was widely hailed and earned the actor several award nominations, including nods at the Golden Globes and Screen Actors Guild Awards. He soon followed with a nomination for Best Performance by an Actor in a Leading Role at the 80th Annual Academy Awards.