Indispensability. This is it. The final dividing line. The quality that separates actors we like, or even love, from those we feel are irreplaceable. A star convinces us that he's filling a void we didn't know was there; he makes us believe that until he came along, the movie world of which he is now at the center was somehow incomplete. Which brings us back to Taylor Kitsch. Leading-man gigs in expensive films that are designed to be blockbusters are, for emerging stars, the devil's temptation. Last year, Kitsch won two of those roles, and then discovered that a big opportunity is not the same thing as a good part. As fans of Friday Night Lights can attest, Kitsch isn't just good-looking; he's a talented actor with a specific set of gifts behind the dreamy eyes and the baked, Costner-ish drawl. No, he's probably not the first guy you'd cast as Wernher von Braun, but he was born to play the redeemable bastard, the near bum who might or might not—depends on the role—summon the moral courage to do the right thing (a quality Savages tapped into nicely). The soulful loner who gets in his own way: If you don't think that's a rich vein for a movie star to mine, go take a tour through the fifty-year career of Paul Newman.

But movies like John Carter and Battleship pull an actor away from the specific and toward the generic. I don't know where Kitsch ranked on the casting wish lists for those parts, but the point is, those lists very likely existed, and they probably weren't conceived with much attention to anything but physical fitness, youth, nice bone structure, and the ability to form words. The lead role in that kind of movie is the Guy, just like the other roles are the Girl, the Bad Guy, the Sidekick, the Crusty Guy, and the Funny Guy. The Guy is a terrible thing to be. Nobody becomes a movie star by playing the Guy, because there are lots of guys who can play the Guy. You don't want people leaving your film, even if it's a hit, feeling that you were interchangeable with half a dozen other people on the posters in the multiplex lobby. You want them to believe that anyone else in the role would have represented a disappointing compromise. There's your litmus test: If they want you, and they can't get you and, as a result, they have to rethink the part, you're a movie star.

Which brings us back to Channing Tatum, and Magic Mike. (Remember the other guy in the movie? You know, the young guy who played...you know, the Guy? What was his name again?) If Tatum ends up being someone we're still writing and talking about thirty years from now, then this movie, in which he played a young, decent guy who didn't mind temporarily retailing his body on his way to bigger and better things, may be seen as his Rocky. In the film, Tatum did the whole movie-star job: He gave us a piece of who he was while making it clear that it wasn't the only piece. He took a chance. He wove something about himself into the work without ruining its shape. He not only risked ridicule, he owned the risk. He commanded the screen but played well with others. He exposed himself in new ways while making sure to hold something back for later. He laughed at himself and made you laugh with him. And he made it clear that nobody else could have done the job quite the same way. Well done. Now let's see what his long game looks like.

_Mark Harris the author of _Pictures at the Revolution: Five Movies and the Birth of the New Hollywood.