Heath Ledger delivers brilliantly as the Joker (AP)

LOS ANGELES - The buzz over Heath Ledger's performance as the Joker in "The Dark Knight" for the last several months was justified. With his final full film role, Ledger delivers what may be remembered as the finest performance of his career.

A press screening of the "Batman Begins" sequel Thursday night had the audience cackling along with Ledger's Joker, a depraved creature utterly without conscience whom the late actor played with gleeful anarchy.

At times sounding like a cross between tough guy James Cagney in a gangster flick and Philip Seymour Hoffman's fastidious Truman Capote, Ledger elevates Batman's No. 1 nemesis to a place even Jack Nicholson did not take him in 1989's "Batman."

Nicholson's Joker was campy and clever. Ledger's Joker is an all-out terror, definitely funny but with a lunatic moral mission to drag all of Gotham, the city Batman thanklessly protects, down to his own dim assessment of humanity.

Spewing alternate personal histories for how he got the horrible scars on his face, the Joker hides behind distorted clown makeup that looks like a chalk drawing left out in the rain.

The Joker masterminds a series of escalating abductions, assassination attempts, murders and bombings, all aimed at calling out Batman (Christian Bale) and proving to the tormented vigilante hero that they are two sides of the same coin.

"You complete me," the Joker tells Batman, dementedly borrowing Tom Cruise's sappy romantic line from "Jerry Maguire."

Long before Ledger's death in January from an accidental prescription drug overdose, his collaborators on "The Dark Knight" had been describing his performance as a new high in the art of villainy for a comic-book adaptation.

Director Christopher Nolan, reuniting with "Batman Begins" star Bale, told The Associated Press earlier this year that Ledger came through with precisely what he had envisioned for this take on the Joker, "a young, anarchic presence, somebody who is genuinely threatening to the establishment."

"It was though they'd taken the Joker and all the colors, everything of it, and just kind of put him through a Turkish prison for a decade or so," Bale told the AP. "It's like he's gone through that personal hell to come out being this, if you can even call him mad, at the end here."

A best-actor Academy Award nominee for "Brokeback Mountain," Ledger has earned fresh Oscar buzz for "The Dark Knight," which could land him in the supporting-actor race.

Running just over two and a half hours, "The Dark Knight" is a true crime epic. Throughout, the Joker's bag of tricks is bottomless, twisted to the point of horror-flick sick.

"Some men aren't looking for anything logical," Michael Caine's butler Alfred tells Bruce, who's trying to decipher the Joker's motives. "Some men just want to watch the world burn."

Come July 18, when "The Dark Knight" lands in theaters, the world will be watching Ledger burn up the screen.