Marvel's Black Widow: The Real-Life Historical Inspirations
Many of Marvel's cinematic characters have historic roots in myth or sci-fi tropes, such as Thor being a Norse-inspired god and Bruce Banner's exposure to gamma radiation turning him into the Hulk. For others, their story has a much greater historical basis, like Captain America Steve Rogers and his desire to fight Nazi Germany (which at least in the 2011 film precedes his awareness of Hydra). The same is the case for Black Widow, or Natasha Romanoff, who was born, raised, and trained in the Soviet Union. According to Den of Geek, elements of the character like her forced sterilization were not known to have been performed on real female agents.
However, there is a decent amount of truth to how the character's origin and original purpose as an infiltrator are portrayed. There were indeed dedicated institutions meant to train spies in the Soviet Union, with women in particular being allegedly trained to weaponize their sexuality for the purpose of compromising and blackmailing targets (via CNBC). Male and female sleeper agents conducting espionage was commonplace, and something that post-Soviet Russia continued to carry out for decades.
Russia had a real-world Black Widow
The year 2010 turned bad for Russian spies in the U.S. when 10 were apprehended, while a further four managed to evade capture and return to Russia. Despite their apparent failure, it is clear that they were adept at convincing others of their American personas when it at least came to American civilians (via CBS). When agents had families (a mix of selling the deception and genuine chemistry), even children like those of the Foleys stated they were shocked by their parents' Russian origin (via Daily Mail).
Anna Chapman (pictured above) was 28 when in 2010 she was among those exposed as Russian agents — too late to have had any role in inspiring the entire Black Widow character, whose first comic appearance was in 1968. However, she may have to some extent inspired Scarlett Johansson's future portrayal of the character (as her debut in "Iron Man 2" came a month before Chapman's arrest). After all, given Chapman's media portrayal as a redheaded and conventionally attractive Russian spy, who was falsely accused of seducing American political figures to gain information (per The Guardian), she is perhaps as close to a real Black Widow as one can find sans any known martial skills.