Who she is: Black Widow, a.k.a. Natasha Romanoff (née Natalia Romanoff)
Her power: She doesn’t possess any superpowers, but Natasha Romanoff was trained from childhood by top-secret Russian intelligence to be the perfect assassin and spy. Her skills as one of the top KGB agents in the world are what earned her the nickname Black Widow.
Her story: As revealed in Avengers: Age Of Ultron, Romanoff was trained from childhood in a place called the Red Room, where they taught her to ignore emotions and focus on the mission, even sterilizing her to prevent the potential distraction of a child. After she had been in the field for a time, S.H.I.E.L.D. became aware of her (in a separate story she recounts in The Avengers) and sent its own agent Clint Barton, a.k.a. Hawkeye, to dispatch her. Instead he recruited her, bringing her into S.H.I.E.L.D., where she fought alongside Barton. She is sent to assess Tony Stark in Iron Man 2 for his fitness for the Avengers initiative, and then recruits Bruce Banner in The Avengers to help locate the Tesseract. She fights with the team to defeat Loki and his alien army in New York, and stays on as an Avenger, working with Captain America to bring down Hydra (in Captain America: The Winter Soldier) and to defeat Ultron (Avengers: Age Of Ultron). She was last seen in Captain America: Civil War, agreeing to fight under the control of the U.N. but still quietly helping Steve Rogers avoid capture.
Played by: Scarlett Johansson
Currently, Black Widow is: Recusing herself from duty, after betraying Tony’s group in battle.
Where will we see her next? Possibly not until the first installment of Avengers: Infinity War, coming in 2018.