Madame B

Madame B is a posthumous antagonist of the Marvel film Avengers: Age of Ultron. She is a Soviet military commander assigned to work in the Red Room program, and the one responsible for training Black Widow into the ruthless assassin she is well-known today.

She was portrayed by Julie Delpy.

Biography
Madame B was assigned by the KGB to train young Soviet girls into becoming ruthless assassins. During the 1990s, she witnessed a young Natasha Romanoff excelling in martial arts and weapons training for months.

Because of this event, Madame B believed Romanoff could be the next assassin called Black Widow and ensured she received the best training which involves taking down targets, despite Romanoff's reservations over the training course and her worries of failing. During the graduation ceremony, Madame B is disappointed to hear that Romanoff has failed her physical tests, but soon finds out that Romanoff has deliberately failed her tests as she doesn't want to go through the ceremony (which involves sterilization). Realizing this, Madame B puts Romanoff through the ceremony as planned, getting her sterilized before deploying her out in the field to become one of the most dangerous assassins in Russia.

It is unknown what became of Madame B afterwards as she was never seen or mentioned again. And despite Romanoff's great reputation as a dangerous assassin, Romanoff's memory of her experiences and of Madame B. haunted her for the rest of her life, an event that led her to defect from the Soviets and join S.H.I.E.L.D.. Romanoff would later relive the memory (thanks to the powers of Scarlet Witch) during the Avengers' fight against Ultron and his army of Sentinels.