(Covers information from Anderson's universe)
"No. You are so much better than that. I was weak. You cannot afford to be."
Alicia was born to Doctor James Marcus and had a happy childhood, but developed progeria, a rare and deadly disease that caused Alicia to prematurely age at an accelerated rate. Desperate to save his daughter, Marcus began searching for a cure and eventually invented the T-virus, which cured Alicia's progeria. However, the T-virus was discovered to have the effect of turning those who were infected with it into the Undead, causing Marcus to want to discontinue using the T-virus. In response, Marcus' partner, Doctor Alexander Isaacs, had Marcus murdered by Albert Wesker. Alicia barely avoided seeing the murder and was then raised by Isaacs, having become owner of 50% of Umbrella with her father's death.
Co-owner of Umbrella and Isaacs' plot
Alicia led Umbrella with Isaacs for many years, but eventually the effects of the T-virus on her cells faded and her progeria returned. Isaacs eventually proposed using the T-virus to unleash an apocalypse that only the chosen few from Umbrella would survive. Alicia was part of this meeting, but was unable to stop Isaacs' plot as he had too much support. Instead, before going into stasis with the other members of Umbrella High Command and thousands of employees in the Hive, Alicia uploaded a recording of the meeting to the Red Queen, an AI created by Isaacs and based upon Alicia herself.
Awakening and death
Ten years after the Global T-Virus pandemic begins, Alicia is pulled from stasis along with Isaacs by Albert Wesker when Alice, a clone of Alicia, makes her way into the Hive in search of the anti-virus capable of ending the pandemic and saving what's left of humanity. Isaacs reveals the truth about Alice's origins as a clone of Alicia to her as well as revealing his knowledge of Alicia's actions. Alicia realizes that while Isaacs' is a co-owner of Umbrella, Wesker is only an employee and fires him. Alicia's actions enables the Red Queen to drop a blast door on Wesker, crushing his arm and freeing Claire Redfield. As Isaacs' runs away, Alicia urges Alice to go after him as Isaacs only needs to keep the anti-virus out of her reach long enough for the last of humanity to be destroyed to win. Alicia, Claire and the Red Queen all remind Alice that the anti-virus will kill her as well due to Alice having the T-virus within her, but Alice is undeterred.
As Alice and Claire chase Isaacs, Alicia refuses to aid Wesker and instead uploads her memories of her childhood into the Red Queen. Shortly afterwards, Wesker bleeds to death and drops the detonator Alice had left in his hand to explosives she had planted on the stasis chambers of the Umbrella High Command. The explosives detonate, destroying the Hive and killing Alicia and the thousands of Umbrella employees and High Command members within.
The next morning, Alice is shocked to discover that she is alive after releasing the anti-virus. The Red Queen explains that the anti-virus destroyed her infected cells while leaving her healthy cells alone. While both the Red Queen and Alicia were aware this would happen, they wanted to see if Alice would be willing to sacrifice herself, something no Umbrella employee or creation would ever do. The Red Queen then tells Alice about the memories Alicia uploaded to her before her death and shows Alice Alicia's childhood memories, giving Alice the chance to become the woman that Alicia was never able to become due to her deadly disease.
Alicia is shown to be a highly intelligent and compassionate woman. Due to being raised by Doctor Alexander Isaacs following the murder of her father, Alicia appeared to possess a loyalty to him and initially agreed with his plan for "an engineered apocalypse." However, she changed her mind due to her compassion and unable to stop Isaacs directly, secretly uploaded a recording of the Umbrella High Command meeting where Isaacs plan was approved to the Red Queen, knowing it would cause the AI to resist Umbrella and give humanity a chance. After being revived in the Hive, Alicia, despite her frail condition and the apparent hopeless situation, kept her wits about her to help Alice defeat Wesker and Isaacs. She also appeared to accept her death, choosing not to even attempt to flee and instead to die in the destruction of the Hive during which she was shown to completely accept her fate. Before dying, she performed a final act of kindness for Alice by uploading her memories of her childhood to the Red Queen so that Alice could gain those memories and become the woman Alicia never could be. Alicia, along with the Red Queen, also lied to Alice about the effects of the anti-virus on her to test Alice's willingness to sacrifice herself and thus her humanity.
- When talking to Alicia, Alice and the Red Queen, Isaacs and the Red Queen treat the three of them as three different incarnations of Alicia Marcus with the Red Queen being the girl Alicia was and Alice that woman she could've been.
- In The Final Chapter novelization, Alicia is shown to see Alice not as a copy of herself, but more as her twin sister.
- In The Final Chapter novelization, Alice notes during the recording of the Umbrella High Command meeting that Alicia is a woman who clearly holds great power and importance amongst the High Command.
- In The Final Chapter novelization, its Alicia who reactivates the Red Queen following the departure of Isaacs, Claire and Alice, gambling that Isaacs will be too distracted to notice Alicia's actions. In both the novelization and the movie, the Red Queen makes it seem like Isaacs death simply allowed the AI to reactivate itself however. Alice also speculates that once Isaacs is dead, Alicia can countermand his orders and recall the Umbrella forces as the sole owner of the Umbrella Corporation. However, this never happens due to Alicia's death in the destruction of the Hive.
- According to Isaacs, physically at least aside from the premature aging from her disease, Alicia is not much older than Alice appears to be.