"You'll be pleased to hear that all experiments are running smoothly."
— Alex, to Spencer
Alex was raised on the orders of Lord Oswell E. Spencer to become one of a superior breed of humans in his eugenics program. The project involved the abduction of a number of children thought to be of "superior" DNA. The children would then be given the surname Wesker, in honor of the project's head researcher.
Alex, like all Wesker children, was programmed to seek out Spencer, eventually rising to a high position within Umbrella and being made head of the same Project that made her. At some point during her work with Umbrella, a painting was commissioned with her and Albert Wesker, a fellow Wesker child, as subjects.
At some point she was also injected with the same Progenitor virus variant as Albert, but she did not become superhuman, merely surviving it as normal.
On 28 August 1998 Alex made a report on Project W, which stated that before Albert Wesker faked his death, the project was at a 94% rate of success, but after the news of his death, the project went down to just 18%.
On 19 July 2000 Alex arrived on the remote formerly Soviet Union-affiliated Zabytij Island with a large team of researchers led by Stuart. She promised to return industry to the poverty-stricken region and, through charisma and employment opportunities after reopening the island's mines, came to be revered by the natives of the island as their savior. Her researchers came to think highly of her as well, calling her "Lady Alex" and following her without question. In secret, Alex used the employees hired to work in the mines as her personal test subjects to develop the t-Phobos Virus, turning most of them into B.O.W.s.
After the fall of most of Umbrella, Alex continued her work for Spencer, being the last remaining child at his side. The brightest of them all, in Spencer's view and words, "Alex excels at absorbing the abilities of others." Alex was tasked with conducting experiments for Spencer on a research facility on Sonido de Tortuga Island, where she would study Umbrella's viruses in order to elucidate the latent ability of immortality from the Progenitor Virus for Spencer. Alex failed to develop the virus, instead siphoning out resources for personal projects, but reported progress to Spencer in order to keep her supply of resources. Then, in 2006, she abandoned Spencer and the island taking all of the results.
In 2011, Alex sent her private militia to abduct Claire Redfield, Moira Burton, and other TerraSave members to Zabytij Island to be used as test subjects for t-Phobos. While Claire and Moira tried to escape, she taunted them over the PA system, while quoting various works of Franz Kafka. Especially, she is also able to trap fellow TerraSave Members at the same time which she was responsible to activate the siren to lure them out and also taunts Gabriel Chavez who attempts to escape by riding the helicopter before it crashes on the other building in explosion.
When Claire and Moira discovered Neil Fisher's betrayal in TerraSave who is responsible for the attack of their headquarters, Alex later betrays Neil by injecting him with Uroboros virus calling him a lapdog. She also brought up about the Terragrigia Panic seven years ago and Neil is one of Morgan Lansdale's puppet as she left him to mutate. After the duo defeated the mutated Neil, Alex continues to observe Natalia Korda who is inside the capsule stating that she is perfect once she was awaken in six months to act like her as she coughs and it was a prelude to her true birth. Later, she is confronted by Claire and Moira, during which she reveals her true intentions before shooting herself on the head. Her suicidal death cause the whole tower to be activated in self-destruct sequence.
Six months later, Alex barely survives the suicide attempt as she mutated into a feminine-like creature, she now uses a black coat and a mask to conceal her hideous form. She confronted both Barry Burton and Natalia at the storage room of the tower after looking at the photo between herself and Albert. She also recognizes Natalia as she removes her mask finally reveals herself. Barry now asks where his daughter Moira is as she replies that she buries her along the rest of them beneath the mountains which angers Barry. Alex proceeds by summoning Revenants to corner the duo as Barry states that he will kill her later, as he shoots the broken ceiling with his handgun to make a collapsed debris making their escape. Alex manages to ambushes the duo at the abandoned town as she knocks Barry onto the cliff and attempts to kill Natalia by choking her. Alex becomes angered to see Natalia retains her human form while hers is mutated. As Natalia open her eyes, she manages to break free from her grasp making her scream in terror at the glance of her. It is implied that Alex has seen the "Alex's form" of Natalia.
"I understand how you felt, Albert. It's not enough to live. I want to transcend!"
— Alex to Barry and Natalia before she mutates into a grotesque monster after injecting herself with the Uroboros virus
She later taunts the duo again by quoting the words of Franz Kafka as well as Natalia's teddy bear, Lottie. When the duo now confronted her at her secret underground cave, she manages to get the vial dose of Uroboros virus as she overdose herself with it stating about Albert and to transcend as she mutates into a grotesque monster with several tentacles in some parts of her body and an exposed spine which she fights the duo throughout the cave, only to be defeated by Barry temporarily. However, she manages to knock Barry down, making her way on Natalia to exact her revenge, only to be interrupted by Moira. As the trio escapes, she finally mutates herself further as she chases the trio as they exit the cave. As she finally corners the trio she was later shot by Claire while wielding the sniper rifle in a helicopter. Barry decides to finish her off while wielding his magnum and Claire decides to aid him to fight her. As Barry distracts Alex, Claire manages shoot her exposed core with an RPG-7, killing her.
Two years later, Alex's copied consciousness dwells inside Natalia's body, unnoticed by everyone. Natalia is seen reading a work of Franz Kafka, among other articles about Bioterrorism. Realizing her experiment on immortality was a success, Natalia/Alex grins a malicious smile.