Her past is pretty mysterious, but is spelled out pretty well in the first movie - https://youtu.be/mKbgey1gWA0  Basically, she was alive a long time ago. She's like a Russian Captain America/Super Spy/Avenger. She's seen things that most heroes don't even know about. In the movie she'll be starring in, she uncovers a crooked plot to take out important political figures in Russia - which happens to relate to her past. Her voice should be confident, but she has a pretty good sense of humor. When I say Russian accent, I'm talking more Russian-American. In other words, she should sound like she's been living in America for a while and her Russian accent is barely noticeable.