Madame B is a minor antagonist in The Marvel Cinematic Universe. She appears as a minor antagonist in the 2015 film Avengers: Age of Ultron and a background antagonist in Black Widow.
She was an operative of General Dreykov and the former mentor of Natasha Romanoff during her time in the Black Widow program. However, Natasha later defected to America and joined S.H.I.E.L.D., betraying her country.