WARNING: The following contains minor spoilers for Black Widow, now playing in theatres and available for streaming through Disney+ Premiere Access.
While Black Widow has thrust the titular super-spy hero to the forefront of the Marvel Cinematic Universe, she is far from alone. In the film, Natasha Romanoff is joined by her fellow Red Room alumni and surrogate sister, Yelena Belova. While the movie saw her operate as a mind-controlled assassin for the Red Room before joining Natasha, her comic book counterpart has led a far more checkered life.
Although she has recently started teaming up with Natasha in comics, Yelena has frequently operated as an antihero and an outright villain. And In 2005's New Avengers Annual #1, Brian Michael Bendis and Olivier Coipel transformed her into the Super-Adaptoid, a being with the power to replicate the powers of anyone near her, even an entire team of Avengers.
Yelena's life was never easy, but things became worse for her than ever before following an unfortunate encounter with the Avengers and Sauron in the Savage Land. During the conflict, Yelena was horrifically burned by Sauron's flames, and she was offered a shot at revenge while recovering from her wounds. A team of A.I.M. scientists worked tirelessly to rebuild Yelena's body into the new Super-Adaptoid so that she could wage a one-woman war on the Avengers.
When she attacked the Avengers, Yelena left the Sentry defeated in record time, empowered by his abilities. She then turned her attention to Carol Danvers, who was the first hero to realize just what they were all up against. Before she could warn the rest of her team, Yelena only tossed Carol aside, stole her powers and stole those of Luke Cage, Wolverine and Spider-Woman, too. Between all of her powers, Yelena had the Sentry's immense Superman-esque cosmic powers, Danvers' equally impressive slate of powers and Wolverine's healing factor, among others. Where Yelena is usually human, this suite of abilities transformed her, briefly, into one of the strongest characters in the Marvel Universe.
Now with no chance of stopping the Adaptoid up close, the team was left figuring out how to stop her from as far away as possible so as to not give her any further abilities to turn against them. As Yelena tore across the sky pummeling one hero after another, Spider-Man and Iron Man both realized the same thing about her powers. Just as Yelena had stolen the powers of the Sentry, she also stole those of his darker half, the Void. Realizing that this was essentially a ticking time bomb with her, the Avengers simple stalled until the Void revealed itself.
After so much time spent fighting with the Sentry's power, Yelena met with the very real consequences of having them. the Void. Over the years, the Sentry has fought, buried, and come to accept the Void, but he has never escaped it. Naturally, Yelena wasn't going to be able to do so either. The visions of distorted beings and the sound of their broken voices drove Yelena to the brink of madness, leaving her in such a distraught state that her handlers decided to remotely deactivate her. Although this seemingly killed her in the moment, she would later show up alive, still as an operative of A.I.M.
Under other circumstances, Yelena's Super-Adaptoid powers could have made her a tremendous asset as a hero. However, autonomy was kept out of Yelena's reach in this lifetime. While Yelena eventually died during as Secret Avengers mission, a big part of her lived on through a clone that was psychically given her memories, and she's made a more heroic turn thanks to her relationship to Natasha. However, the warmth of human connection was denied to Yelena here, where she was merely another pawn for the masters of espionage in the Marvel Universe.