At age 15, Yelena was chosen as a candidate to become the new Black Widow, as Natasha Romanova was no longer loyal only to Russia. She trained for roughly a decade under Vasilievich Pyotr Starkovsky at the espionage academy known as the Red Room, the same facility in which Romanova had trained. Unbeknownst to Yelena, as she grew older, Starkovsky became obsessed with her, paying another woman, Petra, to don Yelena’s costume and satisfy his desires. Petra eventually became psychotic and killed Starkovsky. It was only after Yelena slew Petra and avenged her mentor that she truly accepted her role as the Black Widow.
Graduating from the Red Room, Yelena became the first student to surpass Romanova’s marks. Eager to prove herself better than Natasha and establish sole claim to the title of Black Widow, Yelena interfered with Natasha’s quest for the "Deathless Frenzy" bio-weapon held by terrorist Col. Khan in Rhapastan. Yelena sought to secure the lethal serum for her superiors and to eliminate her adversary, but Natasha’s experience and superior planning enabled Natasha to outmaneuver her young opponent and complete the assignment in her own fashion, slaying Khan and destroying the entire supply of Deathless Frenzy. Yelena pulled a gun on Natasha, but decided to let her live so they could continue to vie for supremacy.
Wishing to teach Yelena a lesson, Natasha then worked with Nick Fury and S.H.I.E.L.D. on Operation: Validate, which entailed the two Widows exchanging physical appearances. While Yelena was struggling to maintain her identity, Natasha duped Yelena’s superior, Yuri Stalyenko, into revealing his plot to steal nuclear weapons hidden in Hudson during the Cold War. Natasha also showed Yelena that Stalyenko thought of her as an expendable pawn, easily replaced. The two Widows teamed up to bring him down, but a resentful Yelena then attacked Natasha, who explained how she wanted to teach Yelena that espionage was not a game. S.H.I.E.L.D. reversed the process and Yelena returned to the Red Room a little wiser, though certainly no fonder of Natasha.
After some considerable time, she was reinstated at S.H.I.E.L.D. and with the help of some rogue S.H.I.E.L.D. agents and the Savage Land Mutates, began work on an illegal Vibranium mining project located in the Savage Land. Realizing that the reformation of the Avengers was a threat to the operation, Yelena hired Electro to cause a prison break at the superhuman maximum security prison called the Vault in order to cause a distraction and reunite Sauron with his Savage Land Mutates. As the Avengers investigated the breakout further, they decided to hunt down Sauron, leading them to the Savage Land. Upon arriving they were beat down by the mutates, who bound them and revealed their part of the Vibranium operation. Controlling his armor remotely, Iron Man managed to free the Avengers. In a short skirmish that followed, the Avengers proceeded to defeat all of the mutates except Sauron. As Sauron was about to tell them about his part in the operation, Yelena used a sniper rifle and shot him in the head, seemingly killing him. Yelena and the rogue S.H.I.E.L.D. agents then proceeded to try to kill the Avengers, but were unsuccessful. As Yelena and Spider-Woman (Jessica Drew) squared off, a revived Sauron expelled fire from his mouth at Yelena which badly burned her body. Burned and beaten, she was taken to an undisclosed location where a mysterious figure offered to help her get revenge on the Avengers, which she agreed to do.
While still hospitalized and brutally disfigured, the mysterious figure returned to Yelena and revealed he was a representative of Hydra. He brought with him agents from A.I.M., who perform an operation which transforms her into a being similar to that of the Super-Adaptoid. Now calling herself the Adaptoid, she set out toward the new Avengers Tower where she proceeded to copy the powers of all of the Avengers and eventually managed to get the upper hand in the battle. However, Spider-Man and Iron Man realized a way to neutralize her. After a few minutes of fighting the wall-crawler she was bombarded by dozens of Iron Man's suits which were remote-controlled by Tony Stark. Using this tactic, they managed to stop her. The Sentry then used telepathy to cause her to perceive that the Void was right in front of her and make her feel that it would haunt her forever unless she revealed who turned her into the Adaptoid. Elsewhere, realizing that Yelena would soon talk, the Hydra representative ordered her termination. Seconds later at Avengers Tower, Yelena was blown up from the inside, killing her instantly.