Which Avengers character was trained in the Red Room from childhood?

The Avengers character trained in the Red Room from childhood was Natasha Romanoff, also known as Black Widow. In Marvel’s story, the Red Room is a covert Russian program that trained young girls as elite spies and assassins.

Natasha was taken into the program when she was young and subjected to years of intense physical, psychological, and tactical conditioning. The training made her highly skilled in espionage, hand-to-hand combat, weapons, infiltration, and deception. Her past is explored especially in Avengers: Age of Ultron and Black Widow.

The Red Room also trained other Black Widows, including Yelena Belova, Natasha’s adopted sister in the Marvel Cinematic Universe. However, Natasha is the answer most directly associated with the Avengers because she was an original member of the team in the 2012 film and appeared in several Avengers missions.

A common mix-up is answering Yelena, who also trained in the Red Room from childhood. Yelena is a Black Widow and later becomes closely connected to Marvel’s heroes, but Natasha Romanoff is the Red Room-trained character who served as an Avenger and is the canonical answer to this wording.