Jacob Benjamin "Jake" 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.

Gyllenhaal has taken an activist role in supporting 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.

The son of director Stephen Gyllenhaal and screenwriter Naomi Foner, Gyllenhaal's immediate family includes his sister, actress Maggie, who is engaged to actor Peter Sarsgaard, Gyllenhaal's co-star in Jarhead and Rendition. In December, 2006, Jake and his sister escaped a fire that destroyed Manka's, a famed lodge and restaurant in Inverness, California, at which they were vacationing. Gyllenhaal's niece, Ramona Sarsgaard, was born on October 3, 2006. Jamie Lee Curtis is Gyllenhaal's godmother, and he has repeatedly referred to his godfathers being a gay couple. Gyllenhaal himself is the godfather of Matilda Rose Ledger (born October 28, 2005), daughter of Heath Ledger and Michelle Williams, both of whom co-starred with him in Brokeback Mountain. His uncle, Anders Gyllenhaal, is the executive editor of The Miami Herald. His late uncle is filmmaker Robert Achs.

Gyllenhaal dated actress Kirsten Dunst on and off for three years.

Representatives of Jake and Reese Witherspoon, his girlfriend since 2007, have told People magazine exclusively that media reports stating the pair are planning to wed are "lies."

"They are not engaged, getting married or any of the reports," the publicists said.