Jacob Benjamin Gyllenhaal (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 1999's October Sky, followed by the 2001 indie cult hit 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 as a frustrated Marine in Jarhead (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 in the 2004 election, and promoted environmental causes and the American Civil Liberties Union.