As the sole female Avenger, Scarlett Johansson had a bone to pick with Hollywood: not only were there few female superheroes, but they tended to be dumbed down.

So when Marvel Studios brought in another formidable woman for summer action film “Avengers: Age of Ultron,” Johansson, who reprises her role as the feisty Black Widow, was happy to see “a step in the right direction.”

Out in US theatres on May 1, the Walt Disney Co film reunites Black Widow with 2012’s “The Avengers” superhero ensemble of Iron Man, Thor, Captain America, the Hulk and Hawk-Eye as they fight a villain bent on large-scale destruction.

Now comes Scarlet Witch, played by Elizabeth Olsen, one of the most powerful Marvel comics characters, known for her thought-altering magical powers, to join the male-dominated superhero ranks. Three other women play key roles.

Boosting the female quotient makes sense as women fans could help push “Age of Ultron” past its predecessor at the box office and possibly make it the top-grossing film of summer 2015.

The film throws a larger spotlight on its female characters, led by Johansson’s Black Widow holding her own in complex fight scenes and finding romance with Hulk (Mark Ruffalo).

The evolution of female characters in Marvel’s superhero movies “has been slow,” Johansson said, since she took the helm as Black Widow in 2010’s “Iron Man 2”.

“We haven’t really been able to explore the depth of the character behind the superhero – that’s what makes characters interesting,” she said.

“It’s nice to see the introduction to Scarlet Witch, and I know that there will be more to come.”

‘Such badasses’

Ever since Marvel’s cinematic franchises became box office hits, starting with 2008’s “Iron Man” starring Robert Downey Jr., superhero films have drawn criticism for not having enough women amid star-studded casts.

“It’s amazing to have two female characters on a poster for a superhero movie,” Olsen said. “Also we’re both portrayed as such badasses.”

For box office expert Paul Dergarabedian, ramping up the female perspective is “vitally important” as female filmgoers make up a bigger share of ticket sales.

“Action movies are not just for men anymore,” said Dergarabedian, senior media analyst at box office tracking firm Rentrak.

“The Avengers,” the third-highest grossing movie of all time, opened in 2012 with a record $207 million in US and Canadian ticket sales.

Forty percent of the opening weekend audience was female, according to a Disney survey at the time.

Disney promoted “Age of Ultron” to female audiences, sending cast members to TV shows such as “Ellen” and “The View”.

It created a line of women’s wear inspired by the female stars that includes a replica of Johansson’s Black Widow jacket.

Johansson showed the power of female-led action films with her non-Marvel flick “Lucy” that grossed more than $450 million worldwide last year.

But there are no plans for a Black Widow standalone film in Marvel’s upcoming five-year plan.

Fans will have to wait until 2018 to see the studio’s first movie led by a female superhero, “Captain Marvel”.

For Joss Whedon, who wrote and directed both “Avengers” films, writing female characters wasn’t “necessarily an agenda” for “Age of Ultron”.

“Everybody who is in the movie is usually the best version,” said Whedon. “Dr Cho (Claudia Kim) is the best doctor in the world, and Maria Hill (Cobie Smulders) is the best agent.”

“They’re that smart, they’re that good – doesn’t matter if they’re a man or a woman.”