The character of Black Widow/ Natasha Romanova is played by Scarlett Johansson, reported Digital Spy.
"I'd like to see her whole beginning story that we hear about (in Avengers: Age of Ultron)," Ruffalo said referring to the scene in which Natasha describes her dark past to Bruce Banner.
"It's so fascinating, her being raised from the very beginning as just a killing deception machine, and how she comes to be with (the Avengers) and how she finds her morality. It would be amazing," he added.