Jacob Benjamin "Jake" Gyllenhaal (pron-en?d??l?nh??l; born December 19, 1980) is an American actor. The son of director Stephen Gyllenhaal and screenwriter Naomi Foner, Gyllenhaal began acting at age ten. He has appeared in diverse roles since his first lead role in 1999s October Sky, followed by the 2001 indie (independent film) cult hit (cult following) Donnie Darko, in which he played a psychologically troubled teen and onscreen brother to his real-life sister, actress Maggie Gyllenhaal. In the 2004 blockbuster The Day After Tomorrow he portrayed a student caught in a cataclysmic global cooling event, alongside Dennis Quaid as his father. He then played against type (typecasting (acting)) as a frustrated Marine (United States Marine Corps) in Jarhead (Jarhead (film)) (2005). The same year, he won critical acclaim as Jack Twist in the film Brokeback Mountain opposite Heath Ledger.

Gyllenhaal has become an activist, promoting various political and social causes. He appeared in Rock the Vote advertising, campaigned for the Democratic Party (Democratic Party (United States)) in the 2004 election (United States presidential election, 2004), and promoted environmental (environmentalism) causes and the American Civil Liberties Union.