HOLLYWOOD – Actor Robert Downey Jr. is eager to share his theory of why superheroes are now so prominent and popular at cinemas across the United States.

“Young kids turn on the news and see all these real-life supervillains,” he tells The Japan Times. “Like the terrorists, those guys who — in the name of their religion — go around blowing up innocent people of other religions. Maybe the kids act blase about it, but that’s acting, trying to be cool. It’s a tough, mean old world out there — old religions, old hatreds.”

Downey, 47, says his new film, “The Avengers,” uses a sure-fire formula that alleviates the fear from all this real-life villainy: Take the heroes from the Marvel films of the past few years and bring them together for a guaranteed blockbuster. It’s like the Traveling Wilburys of action flicks.

The plot centers on the Tesseract, an incadescent cube of immense power that Captain America (Chris Evans) pried from the Nazis in his eponymous debut film last year. It has been retrieved from the ocean floor by Loki (Tom Hiddleston), who is the brother of Thor (Chris Hemsworth) and was also the villain in 2011’s “Thor.” The cube must be removed from Loki’s grasp, so agents Nick Fury (Samuel L. Jackson) and Natasha Romanoff (aka Black Widow, played by Scarlett Johansson) recruit a quartet of superheroes to — you guessed it — save the world. The foursome includes Captain America, Thor, the Incredible Hulk (Mark Ruffalo) and Iron Man, the immensely popular character that Downey first portrayed in the 2008 box-office hit of the same name directed by Jon Favreau.

“What you have in ‘The Avengers’ is Mount Olympus,” Downey says. “A pantheon of gods with sort of one goddess (Johansson). I’m surprised as anyone that ‘Iron Man’ has made me, what, iconic? (Grins) Is it too shaming to keep using that word?”

“Iron Man” and its sequel have grossed more than $1.2 billion and a third chapter is set to be released next year. On top of that, Downey has found success playing the title character in a pair of “Sherlock Holmes” films directed by Guy Ritchie.

“I’m no longer that surprised by the (“Iron Man”) phenomenon … but I’m a little tired of the question, ‘How much longer can you keep playing him?’ Like instead I’ll have to keep playing Sherlock Holmes for as long as old Basil Rathbone did? My agents and I will eventually figure that question out.”

One thing Downey’s team has figured out is that it’s definitely profitable to play the good guy. The actor has had a long history in Hollywood with many well-publicized troubles. He took his first bow at age 5 in his father’s film “Pound,” playing a sick puppy. While he won’t comment on his early career or childhood, between 1996 and 2001 Downey was arrested several times on drug-related offences and spent nearly a year in a California state prison that included a substance-abuse treatment facitily.

After years of struggle, though, Downey was able to get sober and get work. One of the people he is reportedly indebted to for his second chance is actor Mel Gibson, his costar in the film “Air America” (1990). He has defended Gibson during the actor’s own well-publicized scandals and is reluctant to get into a discussion about it during the interview.

“It’s not something I want to get on a platform about here, with all these superheroes to talk about — like, I think Chris Evans is a knockout Captain America — but I’ll just say that when I get along well with somebody I work with, I can be loyal. It’s not like we sit around together philosophizing.”

Would Downey appear in the inevitable “Avengers” sequel? “For how much?” he deadpans. The downside to being Iron Man, he explains, is gaining muscle.

“Anybody can gain plain old weight, and looking around the United States, I’d say most seem to be doing it. I love food as much as anybody … some people have an oral streak. But gaining muscle takes work, man! Muscle weighs more than fat, so you can have two guys at 180 (pounds, 81 kg) and one is overweight while the other is in great shape and looks like he could bend iron.”

Downey had to gain 10 kg of muscle for the role. How? He groans, “You don’t want to hear. I don’t want to go all over it, but it involves lots of repetitions and gym work. If your trainer’s a bore — it’s worse.”

Scarlett Johansson joins the boys’ club in the role of Natasha “Black Widow” Romanoff, a character she has played in most of the Marvel films leading up to “The Avengers.” The actress, who rose to fame in the films “Lost in Translation” and “Girl with a Pearl Earring,” refutes the idea that her character is a mere Girl Friday tag-along.

“She has a past (as a former Russian spy) and she’s no pushover,” snickers the 27-year-old actress. “But you have to remember, (the plot is) from a comic book designed mostly for boys. I thought it would be a fun project, and one where I’m not carrying a bigger burden.”

Johansson also doesn’t worry about being typecast through her repeated (and hopefully future) portrayals of Black Widow. She believes it lets her do more substantive roles (she mentions her upcoming film “Under the Skin,” a psychological thriller with sci-fi touches).

“I like to enjoy what I do and my situation as Natasha has been fun,” Johansson says. “It’s sort of camp, and I get to bang some heads. It’s something I can do now that maybe in 10 years I wouldn’t — I mean, if I’m asked to in 10 years (laughs).”

Johansson’s childhood in New York bore little resemblance to Downey’s.

“We weren’t very affluent at all,” she says. “(I was) just one of the kids, with chores and stuff.” Johansson has two older siblings, an older half-brother and a twin brother named Hunter.

“I think brothers made me more assertive, which came in handy when I got to Hollywood,” she says. “Because if you’re not — forget it. It’s such a rough business. Being blonde or attractive means almost zip in the beginning. You have to keep proving and asserting yourself. … I’d keep reminding myself I have a twin brother and wondered how he’d react to such-and-such a situation. Sometimes that helped get me through.”

Along with “Under the Skin” (due to be released Stateside by the end of the year), Johansson will take on the role of Janet Leigh in “Hitchcock,” set for release in 2013. Leigh, of course, starred in director Alfred Hitchcock’s film “Psycho.”

Johansson isn’t too forthcoming on the details (“I’ve gotten burned when I’ve done that. You find out it’s better sometimes to say not enough than too much”), but is excited about portraying a real-life person whose own character became iconic.

“One of the interesting things about (Leigh) is that first she was overshadowed by being married to (actor) Tony Curtis,” she says. “Then when she got out from under his shadow, she played a fairly small role in ‘Psycho,’ which was an enormous hit and typecast her as a victim.

“That movie’s success was great for Hitchcock … but it wasn’t very good for its actors, like her and Anthony Perkins. I do feel a bigger responsibility acting somebody who really existed.”

Johansson’s turn as Charlotte in Sofia Coppola’s “Lost in Translation” put her firmly on Hollywood’s radar in a wave of critical praise and awards. The film has gone on to be a must-see for Japanophiles and the actress looks back fondly on the experience.

“I remember wondering, before I read the whole script, if my character wasn’t there just to be an affair for Bill Murray — you know, the American male abroad. And ‘the girl,’ ” she says. “But it was a great script, and I got to play a rounded, three-dimensional individual, with her own relationship and limits and standards … and her own growth.

“I think the script’s integrity came from Sofia (Coppola, the writer-director). Women filmmakers don’t necessarily understand women better, but they give female characters their due.”

Johansson also adds that the film’s Tokyo setting had a signifficant impact on her.

“When you grow up in a big country (like the United States), you tend to imagine it’s the whole world,” she says. “It would be so insightful and broadening if every American could spend some time in Tokyo — it’s kind of awesome to be in a major city where you’re one of very few. Where, for a change, you’re the minority.

“But I also remember being in Tokyo and wishing I could connect with more people, get to know them and how they live. People would stare at me, maybe because I’m blonde. But I felt a bit lonely at times, because I was a foreigner and I was an actor. It was being set apart, not being able to get immersed in the place, in the culture, to know and talk to the people. … I wish I knew people there — and I do want to go back.”

“The Avengers” opens nationwide Aug. 14, and will be reviewed on next Friday’s Re: Film page.