Viggo Peter Mortensen Jr. (Danish: [ˈviko ˈmɒːtn̩sn̩]; born October 20, 1958) is an American actor, musician, and filmmaker. He is the recipient of various accolades, including nominations for three Academy Awards for Best Actor, three BAFTA Awards, four Golden Globe Awards, and an Independent Spirit Award.

Mortensen made his film debut as Moses Hochleitner in Peter Weir's 1985 thriller Witness. Through the early 2000s, Mortensen played supporting roles in a variety of films including the historical romance The Portrait of a Lady (1996), the action drama G.I. Jane (1997), the crime drama A Perfect Murder (1998), and the comedy 28 Days (2000).

Mortensen gained international attention for his breakthrough role as Aragorn in the fantasy trilogy The Lord of the Rings (2001–2003). He later starred in several David Cronenberg films including A History of Violence (2005), Eastern Promises (2007), for which he was nominated for the Academy Award for Best Actor, and A Dangerous Method (2011). He gained additional Academy Award nominations for his leading roles as an anarchist father in Captain Fantastic (2016) and as Tony Lip in Green Book (2018). Mortensen made his directorial debut with Falling (2020), in which he also starred. Falling was nominated for the Goya Award for Best European Film.

In addition to film, Mortensen has pursued a variety of artistic endeavors including painting, poetry, music, and photography. Mortensen composed and performed music for films including The Lord of the Rings soundtrack, and has collaborated with guitarist Buckethead on several albums.

In 2002, Mortensen founded Perceval Press to publish his works and the works of little-known artists and authors.