Ledger, left, and Williams separated
last year [EPA]

Kevin Rudd, the Australian prime minister, led the tributes, saying it was a tragic to lose "one of our nation's finest actors in the prime of his life".


"Heath Ledger's diverse and challenging roles will be remembered as some of the great performances by an Australian actor," he said.

Nicole Kidman, a fellow Australian, called it a "terrible tragedy". The actress said: "my heart goes out to his family".


Ledger was nominated for an Oscar in 2006 for his performance as a gay cowboy in Brokeback Mountain.


He was married to Michelle Williams, the US actress who played his wife in the film, but they split up last year. They have a two-year old daughter.


'Stressed out'


In his most recent film I'm Not There, Ledger plays one of the many reincarnations of singer Bob Dylan.


Ledger had also finished filming his role as the arch-criminal The Joker in The Dark Knight, a sequel to the 2005 Batman Begins.


In an interview with the New York Times in November last year, Ledger admitted to being stressed out during the making of the I'm Not There and was on sleeping pills while playing The Joker.


"Last week I probably slept an average of two hours a night," he told the Times; "I couldn't stop thinking. My body was exhausted, and my mind was still going."