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.

Born in Watertown, New York, and raised mainly in Argentina and New York, Mortensen made his film debut in a small role in Peter Weir's 1985 thriller Witness. He went on to play supporting roles in several notable films during the 1990s, including The Indian Runner (1991), Carlito's Way (1993), Crimson Tide (1995), Daylight (1996), The Portrait of a Lady (1996), G.I. Jane (1997), A Perfect Murder (1998), A Walk on the Moon (1999), and 28 Days (2000).

Mortensen gained international attention for playing Aragorn in the fantasy trilogy The Lord of the Rings (2001–2003). He gained acclaim for his collaborations with filmmaker David Cronenberg in the thrillers 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, and which was nominated for the Goya Award for Best European Film.

Aside from acting, Mortensen has explored fine arts, photography, poetry, and music. In 2002, he founded the Perceval Press to publish both his works and the works of little-known artists and authors. Mortensen sang and composed for part of The Lord of the Rings soundtrack and has collaborated with guitarist Buckethead on several albums.