But is he?
Cruise definitely is the guy who rang up $3 billion at the domestic box office since the early 1980s, making him one of the most enduring hitmakers in Hollywood history.
He's also the guy who veered into his own personal bizarro world with Scientology rants that alienated or even offended fans and his love-drunk bouncing act on Oprah Winfrey's couch as he proclaimed his devotion to Katie Holmes.
His box-office returns soured, and he made some career choices which, while not disastrous, were not the sort to restore a stumbling star to the audience's good graces.
"The short answer is, I hope not. Those challenges have been there, but I think he has moved past that," said Chris Aronson, head of domestic distribution for 20th Century Fox, the studio behind "Knight and Day." ''I think he still is the guy. If you look over the course of history, there are very few actors who are the guy as long as he has been and are still rolling along."
"Enough time has passed, and he has tried to make amends," said Chuck Walton, an editor for movie-ticket Web site Fandango.com. "This is sort of the perfect summer movie vehicle for him. I think most, if not all, is forgiven. ... Look at Robert Downey Jr. He's had plenty of things in the past and it hasn't stopped him."
The movie reunites Cruise with "Vanilla Sky" co-star Cameron Diaz. Known for a tireless work ethic, Cruisehurled himself into action scenes that could have been handled by stunt men and continually added spontaneous flourishes to his character, said "Knight and Day" director James Mangold.
The "I'm the guy" exchange was Cruise's invention, Mangold said. Diaz's June Havens, who restores classic cars for a living, has just had a near-fatal encounter with Cruise's Roy Miller, a secret agent who might be a good guy or a rogue spy gone bad.
When Roy reappears in her life, June stammers to her ex-boyfriend, "This is the guy." Cruise riffs off that line and delivers a memorable moment as Roy beams and agrees, repeating "I'm the guy" like a mantra.
"None of that was written. It was just Tom overhearing her and just flowing, creating a vibe on the set," Mangold said. "'I'm the guy. Hey, I'm the guy.' You realize on how many levels this was true. He is the guy in the movie. He is the spy, he is the romantic lead who will sweep her off her feet.
"He's also just the guy. 'I am Tom Cruise, and I am here, and I will knock it out of the park.'"
Whether "Knight and Day" will be a home run or a swing and a miss is in the hands of fans now. Distributor Fox feels it has a good movie, but "Knight and Day" is a tough sell, an original story not based on a comic book, video game or other property with built-in familiarity.
Besides the uncertainty of Cruise's box-office pep, "Knight and Day" arrives during a fitful summer for Hollywood, when known quantities such as "Sex and the City 2," ''The A-Team" and Russell Crowe's "Robin Hood" failed to live up to expectations.
Already stung by weak returns for "The A-Team" and "Marmaduke," Fox has scrambled to build buzz for "Knight and Day" with sneak peak screenings last Saturday in about 500 theaters. The studio also moved up the release date by two days to this Wednesday, hoping audiences will talk up the film and boost ticket sales through the weekend.
Opening weekend often is a make-or-break deal. But "Knight and Day" has it harder than most movies, sandwiched between two of the season's biggest releases, last weekend's blockbuster "Toy Story 3" and next week's hotly anticipated sequel "The Twilight Saga: Eclipse."
If "Knight and Day" does not find an audience this weekend, it probably never will.
"Everybody's nervous about every movie this summer. If 'Sex and the City' or a Russell Crowe movie underperform, why wouldn't you be worried about a film like 'Knight and Day'?" said Paul Dergarabedian, box-office analyst for entertainment Web site Hollywood.com. "There are no sure bets anymore. The audience is so fickle that you just don't know."
Cruise turns 48 next month, and while he retains his boyish good looks, it's hard to maintain an action career at that age and beyond, particularly with the personal baggage dogging him.
As his public image sagged in 2006, "Mission: Impossible III" came out to some of the best reviews in the series, yet it took in just $134 million, by far the worst return for the franchise.
Cruise has done serious roles, earning Academy Awards nominations for "Born on the Fourth of July," ''Jerry Maguire" and "Magnolia." His three films since "Mission: Impossible III" showed new sides to the actor, with middling results.
He drew praise for a hilarious supporting role in "Tropic Thunder," playing a bald, foul-mouthed studio boss.Cruise reprised the character at the recent MTV Movie Awards, and he's planning to play him again in a big-screen spinoff.
Cruise critics gleefully laid in wait to mock "Valkyrie," his World War II Nazi saga in which he donned an eyepatch to play the German colonel who led an assassination attempt on Adolf Hitler. But the movie wound up getting decent reviews, and while it was not a big hit, it did respectable business.
A fourth "Mission: Impossible" installment is in the works, though coming after "Knight and Day," even Cruisefans think he needs to focus less on the spy game and find more diverse roles.
"When I first heard about 'Knight and Day' being put into production, I thought, another spy movie," said Daniel Hubschman, content coordinator for Hollywood.com and a Cruise fan since he saw "Top Gun" at age 7. "I would like to see Tom Cruise move away from spy action. Whether it's comedy, straight-up action, sci-fi action. That's the one thing that might detract from this movie."
Even if "Knight and Day" flops, the film reveals that he has not lost the magnetism that made him a star in the first place. He will have other shots to restore his box-office trajectory, whether with "Mission: Impossible IV" or some other project.
"I saw my first Tom Cruise movie when I was in high school. I've grown up with him as a star of my generation, and THE star of my generation," said "Knight and Day" director Mangold. "With his talent and uncanny relationship with the camera, he's one of the few true movie stars in the last century of film."