Is that Tom Cruise? Is that a Woody Allen Film? What's the big secret?

Woody Allen (right, with Javier Bardem, Penélope Cruz, and Scarlett Johansson) is downplayed in publicity for ''Vicky Cristina Barcelona.'' (Victor Bello/The Weinstein Company)

If a celebrity isn't publicized, does he really exist? Two new movies force the question.

"Tropic Thunder" opened Wednesday, and although Ben Stiller, Robert Downey Jr., and Jack Black are the names listed above the title, the performance everyone is talking about - the only performance that earned applause after a recent screening - was Tom Cruise's extended cameo as the monstrously porcine studio executive Les Grossman.

"Vicky Cristina Barcelona" opens today, and while the faces on the screen are those of the very bankable Scarlett Johansson, Penélope Cruz, and Javier Bardem, many people will be astounded by the fact that it's Woody Allen's most engaging movie in years, better even than his overrated "Match Point." (Granted, my colleague Wesley Morris is less enthusiastic. Everybody's a critic.)

Here's the catch: Judging by the publicity for both films, you'd have no idea that Cruise is in "Thunder" or that Allen wrote and directed "Vicky." The former's name and face appear nowhere in the trailers, poster, or on the promotional website for the $100 million comedy-action blockbuster, and while Allen does get a credit for making his movie, it's in teeny-tiny letters at the bottom of the "Vicky" poster and at the end of the trailer. (He's more of a presence on the film's website, but only after you get past the homepage.)

Why the cone of silence? In terms of box-office returns, Cruise remains one of the most successful actors in movie history. Allen has been nominated for 21 Oscars over the course of his career and has won three. Why aren't their names being used to sell their movies? Why doesn't the marketing department want us to know they're there?

Tom Terrific first. While he can still sell a straight-up action film - "Mission: Impossible III" grossed $134 million in 2006 and "War of the Worlds" made $234 million the year before - Cruise has been floundering in the public eye ever since he fired long-time publicist Pat Kingsley in 2004 and installed his sister as a replacement. Everything followed from that one hubristic act: the bouncing on Oprah's couch, the manic interviews, the verbal fisticuffs with Brooke Shields over psychiatry, the in-house Scientology video leaked onto the Web. Cruise even lost his long-term production deal with Paramount because, in Viacom chairman Sumner Redstone's words, his "conduct was unacceptable." Within a few years, the star went from being Teflon Tom, Hollywood's can-do guy and a real-life action hero (remember when he was rescuing people from muggings and fires in the 1990s?), to a figure of public mockery - the poster child for wiggy Hollywood self-delusion.

The Internet played a large part - that couch dance will unspool on YouTube forever - as did the unraveling of mainstream star power that the Internet represents. Why worship a Hollywood idol when you can celebrate yourself in front of the whole planet on Facebook? There was the sense, too, that Cruise's time was over, and that the leading-man idealism he had embodied since coming to prominence in the Reagan era simply made no sense in the all-ironic-all-the-time environs of the 21st century.

"Tropic Thunder," then, lets Cruise do something remarkable: show that he's in on the joke. Subverting his aquiline good looks under heavy padding, thick glasses, a baldie wig, and enough body fur to render him an honorary Wookiee, Cruise pops up at various points in the movie to shriek invective at the main characters, get jiggy to Flo Rida's "Lo," and basically act out the worst possible caricature of a power-crazed Hollywood suit. (There's also an unacknowledged ethnic edge that may be the role's most breathtakingly taboo aspect. The News York Times' Manohla Dargis wasn't wrong when she labeled what Cruise does here "Jewface.")

By showing he can play as funny and - this is important - as nasty as Stiller, Downey, and company, Cruise proves he's still one of the boys. His appearance in "Tropic Thunder" was supposed to be the film's big secret, but the cat was out of the bag late last year, when photos of the star getting into his fat suit turned up on the Web. In April, the Times reported on a rapturous industry reception for the film and, in particular, for Cruise's Les Grossman.

That's important, too: With "Tropic Thunder," Cruise gets to show the industry as well as audiences that he can mock himself. The performance is a deliciously broad send-up of power-mad Hollywood entitlement as it applies to producers, movie stars, and anyone else who has personal nutritionists and isn't afraid to use them. The "secrecy" is part of the larger gag: If Cruise's presence were announced upfront, ahead of the title, the ploy would look as calculated as it in fact is. Keeping it guerilla renders it hip, and the genius of Cruise's stealth performance is that it shatters his nobly dull early image, nullifies the talk-show weirdo, and repositions his persona for the self-aware modern era. Rather than acting, the actor appears to have hacked the movie. The applause that erupts when Cruise's name comes up in the end credits should be music to his ears: It's the sound of forgiveness. And with the star playing a Nazi in the upcoming "Valkyrie" - OK, a good Nazi who wants to kill Hitler - the timing couldn't be better.

Woody Allen is a different case: He hasn't been marketable in years. Or rather, the writer-director-star has been so marketable with such a narrow slice of the demographic pie - those relatively older upper-middle-class moviegoers who A) like talky, semi-challenging arthouse fare and B) have forgiven him for sleeping with and marrying his adopted stepdaughter in the early 1990s - that he can't be sold to anyone else. Oh, and another unforgivable sin: He's old and wrinkly in a popular culture that can't stand the sight of anyone over 50.

Allen's name has been downplayed in the publicity for his movies since 2005's "Match Point," but never before has he been so invisible - you have to read the fine print to know he had anything to do with "Vicky Cristina Barcelona." To a marketer this makes a certain amount of sense. Why court the remaining longtime Woodman fans who rarely go to movies anymore when you can promote Johansson or Colin Farrell or Ewan McGregor to a younger and potentially much larger ticket-buying public? Why sell a sensuous comedy-drama as the work of a perceived dirty old man? In this calculus, the guy who made the movie becomes an active liability.

The funny thing is that for many people "Vicky Cristina Barcelona" is not only the best Woody Allen movie in ages - since 1994's "Bullets Over Broadway," as far as I'm concerned - but one that spotlights his largely unacknowledged strength as a filmmaker: encouraging a talented cast to explore how love can lead us happily yet horribly up a tree.

There are hallmarks of the fussiness that hinders so many of Allen's films - a too-chatty anonymous narrator, an ending that feels overdetermined and cheaply ironic - but something in the Barcelona air has loosened the 72-year-old director up, because the movie's warm and sexy and funny in a way I didn't think he could ever be. Much of this is due to the cast, especially Bardem as a glorious cartoon of a Catalan painter-stud and Cruz as his home-wrecking muse - a goddess of destruction with killer lips. Allen uses Johansson's slightly dazed persona smartly this time (Cristina really isn't very bright), and if Rebecca Hall falls into the common trap of delivering her lines like a female Woody Allen, she also lets her character's yipyap neurosis flow believably into lust.

It all adds up to a charming, and charmingly insubstantial, tale. "Vicky Cristina Barcelona" is a summer vacation rather than a work of lasting art; the movie doesn't really matter, which is why it works. Just as Tom Cruise displays in "Tropic Thunder" that he's capable of wicked irony, Allen shows in his new movie that he knows how to lighten up and let the story tell itself. These are developments worth crediting even if the marketing department doesn't, and they free those names - "Tom Cruise," "Woody Allen" - to be used with new and unforeseeable shades of meaning in the future.

Ty Burr can be reached at tburr@globe.com. For more about movies, go to www.boston.com/movies.