Madame B

"Sloppy.... pretending to fail. The ceremony is necessary for you to take your place in the world."

- Madame B before having Romanoff sterilized. "You've taken everything from me. My reputation is ruined. Now I will ruin you!"

- Madame B's last words before her defeat by Natasha Romanoff.

Madame B is a flashback antagonist in the 2015 Marvel Cinematic Universe film Avengers: Age of Ultron and the main antagonist in the 2023 film Black Widow Lives. She is a former Russian 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. Two years after the events of Avengers: Endgame. she was transported to Sony's Spider-Man Universe. She is the former trainer and archenemy of Natasha Romanoff/Black Widow, as well as the archenemy of Eddie Brock/Venom.

She was portrayed by Julie Delpy.

Training of Natasha Romanoff/Black Widow
Madame B was assigned by General Dreykov to train young Russian 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 developed a certain respect towards Romanoff, believing that she 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 fear 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.

Escape from San Quentin State Prison
Madame B returns in Black Widow Lives as the main antagonist. Having been brought to Sony's Spider-Man Universe, she goes to San Quentin State Prison, and poses as a prison guard. After finding Patrick Mulligan in his cell for unintentionally shooting Anne Weying, he reveals that he's seeking revenge on Eddie Brock/Venom. Madame B opens the cell door, Mulligan agrees to the deal. After the ruse is discovered, Madame B is handed a gun from one of the prison guards that she had killed, and after Toxin breaks a wall in the prison, they find a Ford Crown Victoria Police Interceptor, and use it as their getaway vehicle, with Madame B as the driver as they escape.

Arrival at the abandoned Public Health Service Hospital
After arriving at the hospital in their getaway vehicle, the duo decide on the abandoned hospital as their lair, but not before Eddie and Natasha show up. Madame B explains to them that Natasha will be in all but good hands, but she isn't fooled by that remark. Venom emerges at the same time as Toxin, whereas Madame B draws out the prison guard's gun.

Final battle and defeat
While Venom is battling Toxin, Madame B is fighting her former student. After several blows, Madame B hurls Romanoff through a window and grabs a tank filled with nitrous oxide in an attempt to sedate Romanoff and re-sterilize her, but she grabs the tank and leaves it in the room where it was found. After Toxin's and Mulligan's defeat, Madame B is knocked out cold by Natasha's two batons. After regaining consciousness, Madame B shoots Eddie in his left arm, hoping that he will die from his injury so that Natasha would be emotionally scarred. However, Venom outsmarted her by rebonding to Eddie, saving his life.

Natasha and Madame B continue fighting briefly. During the fight, Madame B reveals that she now wants to re-sterilize Romanoff as revenge for ruining her reputation as a military commander for the Red Room. Romanoff defeats her former instructor by using her Widow's Bite to knock her down onto the floor, then pushes her into an old elevator. Romanoff severed the elevator ropes, causing the elevator to fall and land on the bottom, trapping Madame B inside. It is unknown what became of her afterwards, but due to being trapped, Madame B is presumed to have starved to death alone in the old elevator, karmically forcing her to suffer as Romanoff had suffered during her sterilization.

Trivia

 * According to Sam Raimi, he wanted to give Madame B a well-deserved comeuppance by having her trapped in an abandoned elevator because he did not want her to get away with having Natasha Romanoff sterilized.
 * Although Madame B trained Natasha, she still is proficient with a firearm.
 * All of the Marvel fans are satisfied with Madame B's defeat, because she can now feel the suffering that she brought onto Natasha.