At a young age, Yelena Belova was a candidate for the Red Room, a Russian shadow program that trained elite assassins known as Black Widows run by General Dreykov. From ages three to six, Yelena was part of an undercover scheme during which operatives Alexei Shostakov and Melina Vostokoff infiltrated Ohio in the United States, with Yelena and fellow but older Black Widow candidate Natasha Romanoff posing as the duo's children. Due to her own age, Yelena was unaware of the true nature of her fake family and grew attached to them. In 1996, Shostakov and Vostokoff completed their mission and blew their cover. The team escaped to Cuba. Once they arrived, Natasha showed that she had grown attached to Yelena by trying to prevent her recruitment into the Red Room.
Although both Natasha and Yelena fell within the five percent of recruits that survived the Red Room training, they became separated early on. Natasha was eventually able to defect to S.H.I.E.L.D. and later the Avengers, breaking free of her mental conditioning. Yelena however was part of the next generation, for whom condition was not psychological but rather chemical. She remained in the Red Room until 2016 when on an assignment to recover the antidote for their mental control she became doused with it herself and went on the run.
With no one else to turn to, Yelena mailed the remaining antidote samples to Natasha, who herself was on the run from after defecting from the Avengers due to the enactment of the Sokovia Accords. Natasha found Yelena in Budapest and learned from her that Dreykov was not dead as she assumed, and that the Red Room was still fully operational. Determined to free the rest of the trainees but lacking the means to locate the Red Room Academy, Yelena and Natasha broke Alexei out of the Siberian prison, who in turn led them to Melina, resulting in their "family" reuniting for the first time in twenty-one years.
As part of the plan to bring down the Red Room, they were captured and taken to the floating Academy that served as Dreykov's headquarters. Melina's knowledge of the facility enabled Yelena to escape, recover the antidote samples that were captured alongside them and release it into the group of Black Widows, instantly snapping them out of Dreykov's control. Because Melina had destabilized the structure, everyone was forced to make a frantic escape but Yelena forsook her chance to sabotage Dreykov's escape craft, finally killing him for good. She was rescued by Natasha who, after making the successful landing, said goodbye to her family and tasked them with replicating the antidote and freeing the rest of the Widows across the world.
In 2023, after Natasha sacrificed herself in order to bring back the half of life in the universe vanished by Thanos, Yelena visited Natasha's grave to mourn her. Yelena had come to work for Contessa Valentina Allegra de Fontaine, who sent her after Clint Barton, claiming that he was the one responsible for Natasha's death.
When Yelena arrived in New York, she attacked Clint while he and Kate Bishop broke in to an apartment to retrieve a vintage Rolex watch. The apartment would turn out to belong to Maya Lopez. Yelena attacked Clint and Kate, and her identity was revealed to them as her mask was pulled off. She escaped shortly. 
Later, Yelena broke into Kate's apartment and made mac and cheese. She waited for Kate to get back, where they had a talk about why Yelena was in New York. When Kate found out Yelena was hired to kill Clint, she tried to dissuade Yelena from her assignment, but it would not work. However, Yelena did a bit of spying for Kate and found out that Kate's mom, Eleanor Bishop. And even more stunning, Yelena sent a video recording of Kate's mom talking with none other than Wilson Fisk, or the Kingpin. 
Later at a Christmas party, Yelena showed up to kill Clint. However, Kate saw her and attempted to stop her from getting to Clint. Kate managed to knock Yelena down, at which Yelena complimented her technique. Then she jumped out the window and ran down the building. After Clint and Kate took out all the Tracksuit Mafia men on the ice skating rink, Yelena attacked Clint. When she asked him how her sister died, and Clint told her she sacrificed herself, Yelena told him he was lying and that he was pathetic. Then she proceeded to beat up Clint. After a few more hits, Clint whistled, using Yelena and Natasha's secret whistle. This stopped Yelena and she asked him how he knew that. Clint told her about how Natasha told him all about her, and this proceeded to persuade Yelena not to kill Clint, finally coming to terms with how her sister had died. She then left Clint on the ice. 
- Yelena's favorite song is "American Pie" by Don McClean.
- Yelena's trademark green vest debuted in Avengers: Infinity War as part of the movie's design for Black Widow. Years later when working on the early concept designs for Yelena, Marvel Studios Director of Visual Development Andy Park decided to give the vest to Yelena as a throwback, with Black Widow then showing that Natasha had obtained the vest from Yelena.
- 4 appearance(s) of Yelena Belova (Earth-199999)
- 21 image(s) of Yelena Belova (Earth-199999)
- 1 victim(s) killed by Yelena Belova (Earth-199999)