This undated handout photo provided by The Weinstein Company shows Heath Ledger in Todd Haynes’ “I’m Not There.” Ledger is an overwhelming favorite to become, on Sunday, only the second actor to win a posthumous Oscar for his role as the Joker in “The Dark Knight.”

New York ? It was a decade ago, and director Gil Junger was seeking fresh talent for his upcoming movie, “10 Things I Hate About You.” He’d already seen 250 or 300 kids. In walked a young Australian TV actor looking for work.

After a quick line reading and a bit of improv, “I was stunned,” Junger says now. Certain he was looking at someone with enough raw magnetism to be a movie star, he turned to his casting people. “Hire him immediately,” he recalls saying of Heath Ledger.

Ten years after that teen flick launched his brief but hugely promising film career, Ledger is an overwhelming favorite to become, on Sunday, only the second actor to win a posthumous Oscar. If he does, the words “Oscar-winning actor” will doubtless precede each mention of his name forever.

But beyond that, what will his legacy be?

Will he be remembered by future generations simply as the talented, versatile young actor he was? Or will his sex appeal endure, lumping him with cinematic heartthrobs of the past? Will he be remembered for one role, his leering Joker in “The Dark Knight”? Or will his premature death be the defining memory, making him this generation’s version of ’50s cult icon James Dean?

It’s easy to see why the Dean comparison has been so tempting. Both actors died in their 20s — Dean in a car crash at age 24, Ledger of an accidental prescription-drug overdose at 28. Like Ledger, Dean was known for a provocative kind of charisma, embodied in the famous photos of his misunderstood teenager in “Rebel Without a Cause.”

Both were recognized with two Oscar nominations — Dean’s were both posthumous, for “East of Eden” and “Giant.” And both will remain forever young, with no inkling of how they would have aged or how their careers would have fared.

But in many ways, the two weren’t alike at all.

“Dean was a whole different animal,” says film historian Leonard Maltin. “He became a cultural icon because of the rebel role he embodied, and even the sort of glamorously grisly way that he died. I’d wager that many young people who have posters of him on their walls haven’t even seen his movies.”

Ledger, on the other hand, had no singular screen persona — it was in large part his versatility that set him apart. Imagine another young actor playing Ennis Del Mar, the taciturn, confused cowboy in “Brokeback Mountain,” or the menacing Joker of “The Dark Knight,” with the heartthrobs of “A Knight’s Tale” and “10 Things I Hate About You” thrown in.