The action-filled movie role marked a big change for the actress, who's known more for low-key performances in films like Sofia Coppola's drama "Lost in Translation" or Woody Allen's sly comedy "Vicky Cristina Barcelona."

But Johansson is in fighting form to reprise her role as S.H.I.E.L.D. agent Natasha Romanoff, a.k.a. Black Widow, in Marvel Studios' "The Avengers," due in theaters Friday.

With her bright red hair and latex suit, the Black Widow teams up with Iron Man, The Hulk, Captain America, Hawkeye and Thor to stop the evil Loki from conquering Earth with his army.

Johansson sat down with Reuters to talk about the film, the fighting style she learned for her role and what it was like to master her character's native Russian language.

Q: Black Widow was introduced in "Iron Man 2" but gets far more exposure in "Avengers." How did you expand the character?

A: "At the end of "Iron Man 2," we know she's a part of S.H.I.E.L.D., but we don't know what S.H.I.E.L.D. is. In this film, (director) Joss Whedon and I talked about her past. Who is she? How does she get to be a mercenary? What path do you follow in order to get to that place? We both wanted to see the darker side of her - not just that she's someone who is highly skilled, but why did she have to learn those skills?"

Q: You're in top form physically on screen. What new fighting skills did you learn?

A: "We incorporated this Wushu style (of fighting) when the Widow wields a huge alien gun. That was new and really challenging. I had to learn how to spin it and move it. It was hard because I'd hit myself with it all the time. And it's heavy. You learn (by using) a broom handle so you're like, 'Ah, I got it down, I've mastered it.' Then all of a sudden they're like, ‘Here's the prop' and you're like, 'What? This thing is 20 lbs!' I was so terribly battered. I'd wake up every day in agony but it was a continuous thing, so it became normal (laughs)."

Q: Black Widow also speaks in her native Russian language, which you seemed to nail. Was it difficult to learn?

A: "I had two days, so I had to learn it phonetically. I knew what I was saying but I had to be able to pronounce it and breathe some life into the lines so that it didn't sound like I was repeating some Berlitz tape. We hired this great Russian translator, and she worked with the dialogue coach. She was really expressive, which helped, so my mouth found the words in a way that didn't just sound like I was a parrot."

Q: You often play with hair color in your movie roles. Did you enjoy being a redhead for the duration of the shoot?

A: "It's nice because it allows me to go a bit under the radar - people don't expect me to have that color of hair. I'm always happy when I do it because it's the first step of the process of finding the character again. To me more than anything, the hair color represents a huge piece of work that we dive head first into. And I'm really happy when I can wash it out because then I'm like, 'Yes, It's finished, we actually did it!' Out it goes and you know you've accomplished something."

Q: You're the only female Avenger in the cast. Did your male co-stars treat you any differently because of that?

A: "If anything, the guys weren't as delicate with me as I thought they would be. They like to play hard and always dragged me along for the ride. I'd always come back with battle wounds. But they're a great group of guys. All of us got on so well."

Q: Who did you spend most of your time with on location in New Mexico?

A: "Jeremy (Renner, Hawkeye) because (we share scenes) together a lot. We fight together, so we had to do a lot of our stunt training together. We had the same battle wounds! Tom (Hiddleston, Thor), Jeremy and I spent a lot of time in the stunt gym because we fight so much hand to hand, so we ended up hanging out together. But we all equally had a closeness."

Q: What was the dynamic like with all of you?

A: "We're all fans of each other's work. Some of us have worked together in the past. Chris Evans and I have made three movies together. Sam Jackson and I made three movies together. Mark Ruffalo I've known for quite some time. Every time Robert (Downey Jr.) was on set, it was like, so alive. We're just lucky that there was no diva on set. It was everybody trying to support one another. It was really nice to have that."

(Reporting By Zorianna Kit; Editing by Bob Tourtellotte)

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