The amazing thing is, not only did he deliver the packages using the thinnest disguise imaginable ...

"So, how about that local sports team that I totally follow? Am I right?"

... but absolutely no one caught on that he was Tom Cruise, even when he sat down and had an entire conversation with a total stranger.

"So what are your favorite Tom Cruise movies? Like, if I held this gun to your head, first three that jump to mind."

And yes, Cruise did actually take it upon himself to learn the other half of being a professional killer, i.e., how to actually kill people. He did extensive training with guns, learning how to shoot quickly and accurately, all with live ammo. He got so good that, on set, he was able to draw his gun and shoot helpless extras down in just under three seconds. Luckily, that time they used blanks, but we guess what we're saying is that if Tom Cruise ever decided on a change of career, "faceless killer" is totally in the cards. Incidentally, that's why we didn't make any Scientology jokes.

When a relatively unknown actor named Adrien Brody was asked to do a Holocaust movie, he probably knew that it was going to stretch the limits of his acting ability. When he learned that it was a Holocaust movie directed by Roman Polanski, he might have pooped a little. But although he'd yet to really show his Hollywood chops, Brody managed to win the Oscar for his role, making him the youngest actor to ever do so at the tender age of 29. The film also made him the only American actor who has ever received a Cesar, which is essentially the French version of the Academy Awards.

"Et le Cesar est attribue a ..."

The Preparation:

It's understandably difficult for any wealthy young American to get into the mindset of a Jew who has lost everything at the hands of the Nazis. In order to fully own the role of real-life Holocaust survivor Wladyslaw Szpilman, Brody had to understand what it was like to see his whole world collapse in front of him. To achieve this, he went ahead and actually gave up everything.

And we don't mean that he stopped getting his double-shot espresso delivered fresh every morning from Colombia via helicopter. He gave up literally everything. His cellphone, his fancy Porche, the freaking apartment where he lived ... he even went so far as to break up with his longtime girlfriend just so that when he cried onscreen, it was goddamn real.

"Maybe locking my entire extended family in that death camp was going a little too far ..."

We should also point out that Brody learned how to play the piano from scratch, so there's that, too. He memorized an entire Chopin piece, the one his character specialized in. So when you see him playing a beautiful four-minute piano piece, it's actually Brody's hands playing that tune. The finished film made Brody an overnight star. Of course, after his notorious Oscar acceptance, we can't be sure that the whole thing wasn't a giant scheme to hook up with Halle Berry.

"Everything has transpired as I have foreseen ..."

You can object that real-life soldiers have to live it for a hell of a lot longer than 10 days, but again, keep in mind that these people are used to eating their meals off of the abdomen of a nude Japanese woman. The level of culture shock is pretty hard to imagine. Dye would only refer to the cast by their character names, made them learn basic combat and survival techniques, and even shot at them with blank ammunition. God seemed to be in on the act as well, because on the very first day of field training, it rained like crazy, soaking everyone to the bone and turning the soft earth that they had to sleep on into mud. Eating only old canned rations and having a Marine screaming for them to move double time pretty much drove them to the brink, which helped them bring genuine mental and physical exhaustion to the screen.

Now, we did say that almost every cast member went through this training. Matt Damon, who played the titular Private Ryan, got to skip out on the horror, just showing up at the end of the whole thing with a cappuccino in hand and shooting his part in a mere six weeks. This was a deliberate decision by Spielberg, who wanted the dynamic between Damon and the rest of the cast to have a hint of animosity. After all, their characters spent two-thirds of the film just looking for this one punk-ass kid in the middle of Nazi-infested nowhere. What better way to get actors to act like they hate a character than to actually make them hate the real person playing him? Other than to, you know, just tell them to do it? Since they're actors?

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"Now, to get everyone really intense, Tom Sizemore's going to eat a box of kittens."

The Preparation:

In Pollock, which he also directed, Harris played the world-famous painter Jackson Pollock during the final years of his life. Harris not only spent 10 years working on the film, but made sure to literally become Pollock in every way imaginable. He gained 30 pounds, took up painting in Pollock's trademark drip style (by building a whole art studio in his house), and even smoked Camel cigarettes, the artist's favorite brand. Basically, he stopped just short of devouring Pollock's heart to absorb his soul.

"No, no, I ate it to gain his strength."

That's just the way Harris is -- he kind of has to live it. In A History of Violence, where he plays the villain, Harris wasn't one to let something like "not even being on set" take him out of character. While at a press conference for the movie, a reporter asked him, "What is violence?" His bafflingly furious response (in which he started pounding on the desk and flinging small objects) left everyone silent for a few seconds, thinking, "Shit, that escalated quickly."

And it's not like he's always going for an Oscar here -- while on the set of The Rock, one of the most Michael Bay Michael Bay movies ever, Harris was so mentally involved with his character that he simply refused to stop acting like a hardened, pissed-off war vet. Not only did he refer to Bay as "sir" at all times, but he even managed to make the other people around him refer to him in the same way. And while messing up a take can be frustrating for any actor, Harris absolutely lost his shit whenever he flubbed his lines. Not because he was just a big drama queen, but because that is exactly the kind of rage someone like his character would've had.

Today, Robert De Niro tends to land a lot of comedy roles, playing a parody version of the badass he used to be. But he deserves the rest. At the beginning of his career, he was Martin Scorsese's golden boy, and together they churned out some of the greatest films of all time, such as Taxi Driver, Raging Bull, and Goodfellas. That shit came at a price.

The Preparation:

First of all, to prepare for Taxi Driver, De Niro actually got a hack cab license and ferried people around New York in full 12-hour shifts, despite the fact that the film was as much about actual cab driving as Game of Thrones is about feudal economics.

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"I disagree with your views of Keynesian wage inflation!"

Then, for Raging Bull, De Niro played the role of real-life boxer Jake LaMotta. To make sure the scenes where he beat people close to death were accurate, he trained his ass off almost every day, sometimes with LaMotta himself. De Niro was so intense with his training that he ended up breaking LaMotta's ribs and teeth. Remember, LaMotta was the actual professional boxer.

The real crazy part came after the ass-kicking scenes were shot. For four months, production on the film stopped so De Niro could focus on portraying the fatter, older version of LaMotta by becoming a fatter, older version of himself. During that time, he just ate himself silly, binging on meat, pasta, and anything else that would help him pack on well over 60 pounds of fat.

That's nothing compared to the brutal regimen Martin Lawrence puts himself through.

But perhaps the biggest bit of unreal dedication came with The Untouchables, where De Niro played infamous crime lord Al Capone. Playing the Chicago kingpin called for De Niro to gain weight once again, but he outright demanded that every physical detail of his character be authentic. He had a tailor in Little Italy craft him a handmade wardrobe of Prohibition-era clothing, right down to the silk underwear that Capone would have worn while beating guys' heads in with a baseball bat. This despite the fact that said undergarments never once appeared onscreen. Thankfully.

If you aren't finished with celebrity insanity yet, then check out 4 Great Artists Who Make it Really Hard Not To Hate Them. Or read about 7 Iconic Characters They Saved from The Cutting Room Floor.

If you're pressed for time and just looking for a quick fix, then check out The Most Baffling PSA Ever: Vote Like ... Spider-Man?