LAS VEGAS - This time out, there's no vat of chemicals to explain how Batman's greatest enemy came to be the twisted sociopath known as the Joker.

Heath Ledger's Joker springs full-blown in this summer's "The Dark Knight," the sequel to 2005's "Batman Begins" that was previewed for theater owners Thursday with a clip showing the new movie's opening sequence.

Unlike 1989's "Batman," in which the deranged, disfigured clown appearance of Jack Nicholson's Joker resulted from a dip in chemical goo, "The Dark Knight" starts right in with the bad guy in all his psychopathic glory.

"I believe whatever doesn't kill you simply makes you stranger," Ledger's depraved Joker cryptically tells an accomplice in the opening scenes, in which he pulls off a daring bank robbery.

In an interview at ShoWest, a theater-owners convention where distributor Warner Bros. showed off footage of "The Dark Knight" and the rest of its summer lineup, director Christopher Nolan said it was almost inevitable that the sequel would pit Christian Bale's Batman against the Joker.

"The psychopathic clown, that's an icon to stand with the guy with the ears and cape," Nolan said. "It's just a wonderful visual relationship, and it's a terrifying image."

Long before Ledger's death of an accidental prescription drug overdose in January, the marketing of the movie had focused on the villain's rise to power and his creepy appearance.

There had been speculation among critics and fans that the studio and filmmakers might take a different approach to selling the film in light of Ledger's death, but the marketing has gone on as originally planned.

"I think he'd be very pleased to see we're just moving ahead as is," Nolan said. "If you try to honor somebody, you honor them by respecting their work and putting it out there for as many people to see. He was immensely proud of the work he did on the film. I feel a great burden to present that in an undistorted form."

"The Dark Knight" is due in theaters July 18.

The last time producer Charles Roven saw Ledger was when he showed the actor the very footage that was screened at ShoWest.

Fans have been buzzing over the anarchic style Ledger brings to the role in the movie's trailer, but the actor himself was utterly taken by what he saw of himself on screen, Roven said.

"He was just blown away by his own performance," Roven said. "He said, `Can I see it again?' So he was really, really thrilled."

Bale - reprising his role as the wealthy Bruce Wayne, who moonlights as the emotionally tormented crimefighter - said he watched the footage Thursday with a heaviness of heart over Ledger. But Bale said he hopes the movie will serve as a testament.

"I hope that this can be seen as a celebration of his work," Bale said. "He did a phenomenal job. It was a real joy working with the man. It was a joy knowing him, as well. I liked him a great deal, and I liked also how seriously he took his work."