The cast of "Tropic Thunder" before the hilarity ensues - Jay Baruchel as Kevin Sandusky, Brandon T. Jackson as Alpa Chino, Ben Stiller as Tugg Speedman, Robert Downey Jr. as Kirk Lazarus, and Jack Black as Jeff Portnoy. Photos courtesy of Dream Works Pictures.

It's only two-thirds over, but it has already been a career year for Robert Downey, Jr. The actor, who was married in the Hamptons three years ago and has longtime connections to the area, could find himself in the rare position of being nominated for both Best Actor and Best Supporting Actor Oscars, for "Iron Man" and his newest film, "Tropic Thunder." No matter what happens on the award front, the blockbuster success of "Iron Man" ensures an excellent bottom line for Downey in 2008 and for years to come given the inevitability of sequels.

In "Tropic Thunder," Downey is an African-American soldier fighting in the jungle against drug smugglers. Well, not exactly. He plays an Australian actor who is cast as a black actor, and he gets so deeply into the part that he actually has his skin darkened through a medical procedure and utters lines like, "Ain't nuthin' but a thang."

Director Ben Stiller hard at work.

"Tropic Thunder," opening this week, has already received rave reviews in Rolling Stone, Newsweek, and other outlets. There has also been some controversy thanks to protests by advocates of "intellectually disabled" people who are unhappy that the word "retard" is used in the film, and used more than once. The bottom line, of course, is how well the movie does at the box office.

Veteran actor Nick Nolte plays a Vietnam veteran who has written a book about his wartime experiences, and it is being filmed as a movie. For various reasons, the shoot isn't going well. It is decided that to help the actors focus better, they are to be dropped off into the jungle to be more intimately acquainted with the Vietnam experience, and that's where Kirk Lazarus (Downey), Tugg Speedman (Ben Stiller), Alpa Chino (Brandon T. Jackson), and Jeff "Fats" Portnoy (Jack Black) go. The experience becomes way too realistic when they encounter armed drug dealers who are not at all happy about the intrusion.

By the way, keep an eye out for the most talked-about bit part of the year - Tom Cruise as the bald, volcanic studio chief.

It is Stiller's movie in that he plays the lead, co-wrote the screenplay, and directed "Tropic Thunder." But when he's on screen, all eyes are on Downey. The actor, whose career was almost derailed by drugs, is emerging as one of the most sought-after A-listers in Tinsel Town.

Nick Nolte as Four Leaf Tayback and Danny R. McBride as Cody.

It's about time. He turned 43 in April, but began appearing in high-profile pictures over 20 years ago. After a few Brat Pack appearances, he played the nihilistic drug abuser in "Less Than Zero" (1987) and starred opposite Mel Gibson in "Air America." His peak at the time was playing the title role in "Chaplin," for which he received an Academy Award nomination.

But then life and work became a roller-coaster for the son of filmmaker Robert Downey ("Putney Swope"). Arrests for drugs were followed by stints in rehab and efforts to revive a dwindling career. He seemed to have recovered when he was nominated for an Emmy Award for a recurring role in the TV series "Ally McBeal," but then the show dropped him after another arrest. Finally, there was one more stay in rehab, and that appears to have made a difference.

Mel Gibson paid Downey's insurance (which no company would provide) so he could make the film "The Singing Detective," and that was the beginning of a remarkable comeback in 2004. He shot "Gothika" with Halle Berry, made the action thriller "Kiss Kiss Bang Bang," was cast by George Clooney in "Good Night and Good Luck," and had a pivotal role as the relentless reporter in "Zodiac." His personal life is sailing in calmer waters too: In 2005, he married the producer Susan Levin in East Hampton.

It was a stretch to see Downey as a Marvel Comics action hero, but when "Iron Man" hit the big screen last spring critics and audiences were singing his praises. The film has raked in half a billion dollars on the international market, and DVD sales and rentals will add to that total. Downey has already signed on for the sequel.

Robert Downey Jr as uber-serious actor Kirk Lazarus.

But there are plenty of other projects to do in the interim. Coming out this year is "The Soloist," with Downey in the lead with Catherine Keener and Jamie Foxx. He is making the latest version of "Sherlock Holmes," directed by Guy Ritchie who, for now anyway, is married to Madonna. But this week and next (and next?) all attention is on "Tropic Thunder."

"The whole film is based on the idea that what we actors do at some level is offensive and who we are, at some level, is despicable and pathetic, which is the truth and not the truth," Downey said. "But the part of it that is the truth is entertaining."

What about a white man playing a black man? "It's entertainment that is set up by people who are high-minded enough to not be racist or offensive," he said.

And again, it may well come down to how the audience embraces the film. "Tropic Thunder" is after all billed as a comedy with action mixed in. Ben Stiller had that in mind when he signed up Downey to play Kirk Lazarus. "A white guy playing this black role to challenge himself the most in a way that is wrong-headed and going too far," he said, "to me, that was the funnier idea."