Following roles in Australian movies and TV series, Ledger was cast in his first American film 10 Things I Hate About You in 1999. Following this he appeared in Mel Gibson's Revolutionary War drama The Patriot in 2000 and was given the lead role in the 2001 movie A Knight's Tale. At the time of his death, he had just completed filming the 2008 Batman movie The Dark Knight, in which he plays The Joker. For this part he posthumously received the 2009 Golden Globe Award and the Academy Award for Best Supporting Actor in a Motion Picture (only the second time the Academy Award was given posthumously). Ledger's mother, father and sister were present to accept his Oscar.
Ledger had a relationship with Michelle Williams, who played his on-screen wife Alma in Brokeback Mountain, and fathered a daughter, Matilda Rose, who was born in 2005. The couple were separated at the time of his death.
Ledger was found unconscious in his bed by a masseuse at his rented SoHo (Manhattan) loft apartment on January 22, 2008. The masseuse called Ledger's girlfriend, but did not call 911 until he had stopped breathing, approximately 45 minutes later. The New York City medical examiner said Ledger died "as the result of acute intoxication by the combined effects" of six different prescription drugs: oxycodone, hydrocodone, diazepam, temazepam, alprazolam and doxylamine. Police had said at the time of the discovery of his death that no illicit drugs or alcohol were found in the apartment. It is believed that his overdose and consequential death were caused partly by his acting strategy to portray the Joker in The Dark Knight.