Is this, somehow, the role that killed him?
We've seen high-profile, posthumous performances before, of course, but nothing that's provoked this kind of morbid fascination. (Was anyone looking for clues to Owen Wilson's suicide attempt in "Drillbit Taylor?" Wait, I take that back.)
Warner Bros. has tactfully said nothing on the subject and initially presented Ledger's death as a delicate public relations problem. But as the months have passed, it's looking more and more like a gold mine. A poll of some 8,000 visitors to movietickets.com shows 68 percent list Ledger's performance as the main reason for seeing the movie.
And the truth is that Ledger's turn as the Joker - quite eccentric and quite good - will only intensify speculation about his performance and his state of mind.
As the Joker, his smeared lipstick and electro-shock hair make him look like Bette Davis in "Whatever Happened to Baby Jane," and the movie puts him front and center immediately, giving him a grand entrance.
It's a bank heist, and while the perps wear cartoon masks, the violence is real (almost "Heat" real) and pegs The Joker as a deranged man in love with chaos and death:
"Whatever doesn't kill you," he announces, after much killing, "makes you stranger."
The prologue also establishes The Joker as a loner - the polar twin to Batman's lone ranger of justice. It's why the Joker has contempt for the hoodlums he organizes and exploits, and why he regards Batman as Gotham's only interesting guy and worthy opponent.
The feeling is not mutual.
Batman has issues, but he also has humanity. He's knows, for instance, that he's capable of love. He carries a torch for lifelong friend Rachel (Maggie Gyllenhaal) but stands aside as she falls for DA Harvey Dent (Aaron Eckhart). Why? Because Dent's a crusader who stands behind the rule of law rather than a mask, a true hero around whom Gotham, and Rachel, can rally.
"The Dark Knight" takes this love triangle very seriously. All its characters, even its baroque inventions, are grounded (by director Chris Nolan or by the actors) in psychological realism. And the movie takes place in a real city, not Tim Burton's trippy, nocturnal theme park. The central characters are vulnerable, and some are even perishable.
This ain't a cartoon, folks, and it ain't for kids. Even adults may struggle with its narrative complexity.
Brothers Chris and Jonathan Nolan inherited the script from "Batman Returns," but they've written this one themselves, and it has the puzzle-box intricacy of "Memento" or "The Prestige."
In fact, you get the pledge, the turn and the prestige - and more prestige, still more prestige. Almost as many endings as "The Lord of the Rings: The Return of the King."
I was often exasperated but also astounded that the Nolans would lavish so much attention on story in an age when audiences have demonstrated ("Pirates 2/3," "National Treasure 2") that they don't much care if a blockbuster has one.
It will be interesting to see if today's audiences sit still for this kind of density, or for the Nolans' history lessons about ancient Rome and pointed parables about Burmese bandits.
Less arcane is the movie's interest in the post-9/11 landscape, and the way it links Jokerism with terrorism. Its central theme is how civilization, constrained by ethics, deals with a nihilist who observes no rules.
"The Dark Knight" probes terror and fear with more skill that other recent movies, and even examines specific issues like rendition and illegal surveillance - not with complete disapproval!
"Some men just want to see the world burn," cautions Alfred (Michael Caine) as Batman searches in vain for a method to Joker's madness.
Everything rides on the Joker's formidability as a villain who can carry that kind of weight. In his last role, Ledger makes us believe.