(AP Photo/Jason DeCrow)
There was no obvious indication that the Australian-born Ledger had committed suicide, NYPD spokesman Paul Browne said.
Ledger had an appointment for a massage at the SoHo apartment that is believed to be the home of the "Brokeback Mountain" actor, Browne said. The massage therapist and a housekeeper found his naked body at about 3:30 p.m. They tried to revive him, but he was already dead.
"I had such great hope for him," said Mel Gibson, who played Ledger's vengeful father in "The Patriot," in a statement. "He was just taking off and to lose his life at such a young age is a tragic loss."
Outside the Manhattan building on an upscale street, paparazzi and gawkers gathered, and several police officers put up barricades to control the crowd of about 300. Onlookers craned their necks as officers brought out a black body bag on a gurney, took it across the sidewalk and put it into a medical examiner's office van.
While not a marquee movie star, Ledger was an award-winning actor who chose his roles carefully rather than cashing in on big-money parts. He was nominated for an Oscar for his performance as a gay cowboy in "Brokeback Mountain." During filming, he met Michelle Williams, who played his wife in the film. The two had a daughter, now 2-year-old Matilda, and lived together in Brooklyn until they split up last year.
Though his leading-man looks propelled him to early stardom in films like "10 Things I Hate About You" and "A Knight's Tale," his career took a notable turn toward dramatic and brooding roles with 2001's "Monster's Ball."
In what may be his final finished performance, Ledger proved that he wouldn't be intimidated by taking on a character as iconic as Jack Nicholson's Joker. Ledger's version of the "Batman" villain, glimpsed in early teaser trailers, made it clear that his Joker would be more depraved and dark.
Curiosity about Ledger's final performance will likely stoke further interest in the summer blockbuster. "The Dark Knight" director Christopher Nolan said this month that Ledger's Joker would be wildly different from Nicholson's.
"It was a very great challenge for Heath," Nolan said. "He's extremely original, extremely frightening, tremendously edgy. A very young character, a very anarchic presence that taps into a lot of our basic fears and panic."