John Peter Sarsgaard (born March 7, 1971) is an American film and stage actor. He landed his first feature role in the movie Dead Man Walking in 1995. He then appeared in the independent films Another Day in Paradise (1995) and Desert Blue (1996). In 1998, Sarsgaard received a substantial role in The Man in the Iron Mask (1998), playing the son of John Malkovich's character. Sarsgaard later achieved critical recognition when he was cast in Boys Don't Cry (1999) as John Lotter. He landed his first leading role in the 2001 film The Center of the World. The following year, he played supporting roles in Empire, The Salton Sea, and K-19: The Widowmaker.

For his portrayal of Charles Lane in Shattered Glass, Sarsgaard won the Online Film Critics Society Award in the category for Best Supporting Actor and was nominated for the 2004 Golden Globe Award for Best Supporting Actor. Sarsgaard has appeared in an eclectic range of films, including the 2004 comedy Garden State, the biographical film Kinsey (2004), the drama The Dying Gaul (2005) and big-budget films such as Flightplan (2005), Jarhead (2005), and Rendition (2007).

Sarsgaard has also appeared in Off-Broadway productions including Kingdom of Earth, Laura Dennis, and Burn This. In September 2008, he made his Broadway debut as Boris Alexeyevich Trigorin in The Seagull. Sarsgaard will appear in the off-Broadway production of Uncle Vanya in January 2009. Sarsgaard has been in a relationship with actress Maggie Gyllenhaal since 2002. In 2006, the two became engaged and Gyllenhaal gave birth to their daughter, Ramona, on October 3, 2006. On May 2, 2009 Sarsgaard and Gyllenhaal were married in Italy.