Now the Batman archfiend stands as Ledger's next-to-last performance. And while it's not the first, "The Dark Knight" has already emerged as arguably the biggest movie featuring a posthumous role in Hollywood history.
Major stars including James Dean, Clark Gable, Carole Lombard, Spencer Tracy and Will Rogers had high-profile films released after they died. The deaths of others — notably Bruce Lee and his son Brandon — created an eerie allure that heightened interest in their final films.
Yet none had the magnitude of a comic-book franchise with an illustrious 70-year history, and movies in those eras did not arrive with the fanfare of today. Certainly none had the advance word of a delirious, demented turn by an actor completely reimagining of one of Hollywood's greatest villains.
"It was punk, it was `A Clockwork Orange, it was druggie. It was this kind of fantastic, anarchic look to him. This character who had absolutely no rules whatsoever," said Christian Bale, who returns as rich guy Bruce Wayne and his crime-fighting alter-ego Batman. "That's not like any Joker I've ever seen before, what I saw Heath do."
As the sequel to 2005 blockbuster "Batman Begins," "The Dark Knight" already was one of this year's most-anticipated films. Opening July 18, the film's must-see status has only risen since Ledger died of an accidental prescription drug overdose Jan. 22.
"More people will come to see it because of his death," said Bill Ramey, founder of the fan Web site Batman-on-Film.com. "No doubt some people may be apprehensive about seeing it because there may be a little ghoulish factor about it. But I'm betting that more people now kind of look at it as a tribute to him, and the biggest tribute you could give someone is to go see it and enjoy his performance."
When Dean died in a car wreck in 1955, studio executives lamented "there goes the movie," figuring audiences would be scared away from his final two films, said Wes Gehring, who teaches film at Ball State University. To the contrary: "Rebel Without a Cause" and "Giant" were huge hits.
In today's anything-goes celebrity climate, it's doubtful anyone in Hollywood ever felt Ledger's death might hurt the box-office prospects for "The Dark Knight," Gehring said.
"It's a tacky thing to say, but what would have been a negative in the past now could be a positive thing," Gehring said. "I think we've done a flip-flop on pop culture. Now it might actually be a selling point for a movie where you say, `So and so's dead. Let's go see his movie.' What might have been a hindrance in 1935 now won't be a problem."
In the days after Ledger's death, fans debated how it might affect the film.
Would distributor Warner Bros. make changes or even delay its release? Would the advertising shift away from its early focus on Ledger's demonic Joker and his mocking taunt, "Why so serious?" Would the Joker's ghastly persona disturb fans? Would viewers be able to set thoughts of his death aside as they watch his performance?
"Of course, you find more poignancy in moments, and I'm very, very aware he's not here with us," said Bale in an interview shortly after the film's opening segment -- in which Ledger's Joker orchestrates a bank heist — was screened in mid-March at ShoWest, a convention for theater owners. It was the first time Bale had seen the sequence, and Ledger's death weighed on his mind.
"I can't deny that kind of threw me watching that just now," Bale said. "You can't help but have that different feeling when I'm viewing it, especially since he's somebody I was in touch with until just recently and believed would be a future friend."
Director Christopher Nolan, who revived the franchise with "Batman Begins," said he expects the performance will speak for itself, that morbid thoughts of Ledger's death will not affect the way audiences view "The Dark Knight."
"Having seen the movie myself in such heightened and tragic circumstances, no, I don't think that's going to be the case," Nolan said. "What I found in watching the movie myself is that you're not looking at the actor, you're not looking at the friend, you're not looking at the colleague. You're looking at the Joker. ... He inhabits this character, and it's an extraordinary icon, so it's easy to enjoy it on that level, just as a great piece of acting."
Ledger -- known for serious films including "Brokeback Mountain," which earned him a best-actor Academy Award nomination -- was a surprise choice for the Joker, most famously played previously with Jack Nicholson's giddy performance in 1989's "Batman."
Nolan, Ledger and their collaborators came up with a wildly different Joker, whose ominous clown makeup seems to have been finger-painted onto his face, an outer portrait of the black and twisted soul within.
Ledger's performance floored two-time Oscar winner Michael Caine, who reprises his role as Bruce Wayne's butler, Alfred. Caine's first glimpse of the character came when Ledger emerged onto the set from an elevator; in an interview last September, four months before Ledger's death, Caine said he was so startled that he forgot his lines.
"He came out of the bloody lift like a whirlwind," Caine recalled. "They said, `It's your line, Michael.' I said, `What is it?' Extraordinary. It will be one of the characters of next year, the Joker as played by him."
Warner Bros. executives, who declined to comment for this article, have moved ahead with "The Dark Knight" and its marketing as planned. To do anything differently would have disrespected Ledger's memory, the filmmakers said.
"The greatest testament to Heath's portrayal is to do everything that we were planning on doing with Heath's portrayal," said producer Charles Roven. "His family knew him to feel exactly the same way. They knew how excited he was, knew how much fun he had doing it. When you see the film, it's undeniable how much fun he had playing the character."
While the "Batman" brand-name virtually assures blockbuster status for "The Dark Knight," other posthumous films have had a mixed history.
Rogers scored a posthumous hit with "Steamboat Round the Bend," as did Tracy with "Guess Who's Coming to Dinner."
Bruce Lee's "Enter the Dragon" and Brandon Lee's "The Crow" found broader audiences beyond action crowds because of their deaths. Singer Aaliyah's "Queen of the Damned" overcame bad reviews to become a modest commercial success.
Received coolly by critics, John Candy's "Canadian Bacon" and "Wagons East" were box-office duds, as was Natalie Wood's "Brainstorm."
The final films of Lombard ("To Be or Not to Be") and husband Gable ("The Misfits") earned critical acclaim and have held up over the decades but initially were disregarded by audiences.
Unlike Oliver Reed, whose death during the filming of "Gladiator" prompted the filmmakers to digitally graft his head onto another man's body to complete a scene, Ledger had finished his work on "The Dark Knight."
Ledger died with his final film, Terry Gilliam's fantasy "The Imaginarium of Doctor Parnassus," only half finished. Gilliam salvaged the production by casting Johnny Depp, Jude Law and Colin Farrell for the fantasy portions, each playing Ledger's character on trips through a magic mirror into a parallel realm.
The snippets of Ledger's "Dark Knight" performance released in trailers have captivated not only the average fan, but also his close colleagues from past films.
"You can tell Jack Nicholson was having fun doing that, but you can see Heath probably put his soul into it," said "Brokeback Mountain" director Ang Lee. "That's why it's scary. You see the trailer, just a few shots of him, you have to see the movie. ... I'm anxious to see it. I'm afraid to see it. I don't know how I'll respond to it, but you have to see it."