From killer smile to ... killer?

The bad guy in "Collateral" is a very bad guy indeed - a psychopathic killer who claims his conscience is clear because murdering people is how he makes his living.

What's most unusual about this character isn't his cold-blooded nature.

It's the actor who plays him: Tom Cruise, who had his first phenomenal success as the fresh-faced hero of "Top Gun" and has played other sympathetic roles in such movies as "A Few Good Men," "Minority Report," and "The Last Samurai."

What's a clean-cut superstar like him doing in a role like this? Isn't it "risky business," to borrow the title of an early Cruise hit, to play against his usual upbeat image?

Not really. "There's more than one reason for someone like Cruise to stretch his image this way," says Dan Gurskis, a TV screenwriter. "One is that he's getting older. His years as a conventional leading man could be over soon, so naturally he wants to test the waters of different images. Another is that he wants to be seen as a serious actor, not just a career-oriented star.... Roles like this are a way of showing off his talents."

Cruise is far from alone in wanting to strut his stuff as a "serious actor" - not just another pretty (and aging) face. Former model Charlize Theron hid her gorgeous appearance beneath added pounds and loads of makeup to play a serial killer in the aptly titled "Monster" last year, winning the Oscar for best actress.

Denzel Washington also understands this concept, taking home the Best Actor Academy Award for his corrupt policeman in the 2001 action melodrama "Training Day."

To be sure, Tom Hanks fared less well as a villain in "Road to Perdition" and "The Ladykillers," which may explain why he's scurried back to good-guy land in "The Terminal" and "The Polar Express," his upcoming Christmas release.

Then again, audiences had no problem watching Mel Gibson wax vicious in "Payback," a 1999 movie so eager to showcase Mr. Gibson as a vengeance-crazed thief that its promotional slogan read, "Get ready to root for the bad guy," and the video box banners his photo with, "No more Mr. Nice Guy."

This isn't even the first time Mr. Cruise has strayed from the straight-and-narrow path. He played a raging rebel in "Born on the Fourth of July," morally challenged millionaires in "Magnolia" and "Eyes Wide Shut," and the ultimate villain - a monster of the undead - in "Interview With a Vampire."

Things weren't always like this. A few decades ago, few in Hollywood would have fiddled with a successful star image.

A case in point is the 1941 thriller "Suspicion," an Alfred Hitchcock movie suggesting Cary Grant's character might be a psychopath bent on killing his new wife.

As conceived by Mr. Hitchcock, the movie's ending would have confirmed our suspicions that Mr. Grant's suave exterior masked a murderous secret life.

But not even a filmmaker with Hitchcock's awesome clout could make this appealing to the RKO studio, which insisted Grant be revealed as a misunderstood good guy in the final scene. To the end of his career, Hitchcock regretted what he saw as a missed artistic opportunity.

By contrast, today's film industry is generally open to stars trying on different images, or at least toying with them occasionally.

Otherwise we wouldn't be seeing square-jawed Colin Farrell as bisexual in "A Home at the End of the World," and memories of Julie Andrews's nude scene in the 1981 comedy "S.O.B." might have disqualified her from the currently successful "Princess Diaries" franchise.

Some observers say it's not only safe but downright necessary to play against type in today's competitive movie world.

"Many careers are sitting on a railroad track," says Harlan Jacobson, who hears moviegoers' opinions every week as chief of Talk Cinema, a nationwide sneak- preview series that includes a discussion after each screening. "Look at Tom Hanks or Eddie Murphy," he continues. "Sooner or later, the marketplace tells them - all too clearly - they need to move or die!

"Public tastes change," Mr. Jacobson adds. "So the real risk to stars is being left behind unless they explore and develop."

The outcome is never certain, of course. "There is a chance you'll alienate your core audience if you try something really different," said Paul Dergarabedian, head of the statistical research firm Exhibitor Relations, in a telephone interview.

"It's the same when a comedian does a serious part. People didn't want to see Jim Carrey that way," he adds, referring to "The Majestic," a 2001 flop.

But eventually it all comes down to how high the quality of the movie is, he concludes. "If it's a piece of junk, it doesn't matter what the star does. If it's good, it can transcend the star's conventional image and ... revivify it."

Complicating this issue is the vagueness of what "playing against type" means in the first place.

For example, to one viewer, casting Will Smith in "Ali," the biopic about prizefighter Muhammad Ali released in 2001, would qualify.

To another viewer, though, it seems perfectly appropriate for the gifted and versatile Mr. Smith to play Mr. Ali, himself a gifted and versatile celebrity.

Something similar goes for Mr. Carrey in "The Majestic," where his character is dazed and confused but not unsympathetic or unappealing, and for Meg Ryan in last year's "In the Cut," where she plays a basically decent woman caught up in horrible circumstances beyond her control.

Many reviewers praised these performers (if not the movies) for doing what every actor ought to do - flexing artistic muscles that would get no exercise at all if box-office receipts were all actors thought about.

"What really makes a star a star," says William Hornsby, a film professor at Brooklyn College, "is an innate beauty that's part of [his or her] talent. I love watching Denzel Washington and Gene Hackman because of who they are and what they look like.

"I haven't seen 'Collateral,' " he says, "but I know Tom Cruise will have a full career as he ages because he already has an indelible image, just like Cary Grant and Sean Connery.... When these talents and beauties are real, not manufactured, [a star] can do all kinds of things without leaving the audience behind for a second."

Mr. Dergarabedian says much the same.

"Stars usually want to try new things as they develop more clout in the industry," he says. Those are "often among the most fascinating work they do."