Lisa Trevor was once an ordinary human girl, transformed into a horrific mutant creature after years of constant viral experimentation by the Umbrella Corporation. She appears as a recurring threat in the remake of the first Resident Evil game and during the "Rebirth" scenario in The Umbrella Chronicles.
Lisa was the daughter of architect George Trevor, who had been commissioned by Oswell E. Spencer in 1967 to build his mansion in the Arklay Mountains. Due to the need for secrecy regarding the mansion's purpose, Spencer arranged for George and his entire family to become permanent "guests" within the estate. Jessica and Lisa arrived ahead of George and were apprehended by Spencer's agents, taken down to the laboratory beneath the mansion where they became test subjects for Umbrella's research on the Progenitor virus. George would arrive days later only to be informed that his wife and daughter had left to visit a sick relative. Held prisoner within the estate, George attempted to escape through the catacombs beneath the house, but would die of starvation.
As for Jessica and Lisa, they remained locked away in the laboratory and Lisa was subjected to various invasive and painful experiments. After being injected with Umbrella's initial strain of Progenitor, Lisa gradually began to show signs of mutation, her body being horrendously malformed and her mental state severely impaired. Jessica was also subjected to viral treatments, but after she displayed no reaction to the virus, Umbrella had her terminated.
After being seperated from her mother for so long, Lisa began to grow increasingly violent. Needing to pacify her, the Arklay lab researchers disguised some of their own staff as Jessica as a means of calming Lisa. All of these attempts at pacification failed and Lisa killed every handler assigned to her, ripping off their faces and attaching them to her own body. The increasingly mentally unstable and lonely Lisa grew obsessed with finding her true mother so that she could "give her back her face". Lisa was able to find the secret tomb of her mother, built under the Spencer Mansion. While she was able to recognize the scent of her mother, she was unable to open the stone coffin and "reunite" with her.
As the years passed, Lisa remained locked away beneath the Spencer Mansion, continuously subjected to different viral strains. She survived all of these experiments which continued to wreak havoc upon her genetic structure and her psyche, de-evolving her into an animalistic state. Her incredible survivability attracted the attention of Umbrella researchers William Birkin and Albert Wesker, who attempted to infuse Lisa with the newly-developed NE-α Type parasite and see how she reacted. Lisa overcame the parasite and even ingested it, incorporating its genes into her own. Following this event, Umbrella discovered that Lisa's consumption of the parasite resulted in the cultivation of a new viral strain in her body: the G-Virus.
In 1995, the G-virus was extracted from Lisa's body and Umbrella's interest in Lisa waned. The unstable Lisa continued assaulting and killing the research staff at the Arklay laboratory, and so Umbrella decided to dispose of her. Unfortunately, both for Umbrella and Lisa, the multiple experiments conducted on her had mutated her body to such a degree that she had become immune to seemingly any form of physical assault; gunfire had no effect on her whatsoever and even anti-tank ammunition would only knock her down temporarily. After multiple attempts, Umbrella believed they had killed Lisa and monitored her body for vital signs over several days before finally declaring her dead. Her body was dumped into the catacombs beneath the Spencer estate, but she would revive again and lurk through the catacombs for the next three years without further contact with any of the Umbrella staff.
In 1998, during the fated Mansion Incident, various members of the Special Tactics and Rescue Service encountered Lisa as they investigated the area surrounding the Spencer Mansion. Their attempts to neutralize her proved to be utterly useless as Lisa's seemingly indestructible body absorbed bullet impacts, but during an encounter inside the crypt beneath the mansion, Jill Valentine solved the puzzle of the crypt and opened the sarcophagus inside. Inside the coffin was the skeleton of Lisa's mother Jessica, which Lisa seemed to recognise by scent and even croaked the word "Moth...er..." in response. Taking her mother's skull from the coffin, Lisa then cast herself into the dark abyss beneath the crypt. As far as the S.T.A.R.S. were concerned, Lisa was finally dead, but Wesker would encounter her again as he made his escape from the laboratory following the activation of the self-destruct system. Lisa seemed to recognise Wesker somehow and hounded him as he made his way out of the facility. She pursued him all the way to the mansion's main hall, but Wesker shot down a large chandelier from the ceiling which fell on Lisa. Wesker then made his exit from the mansion and Lisa was apparently killed when the mansion self-destructed.
Behaviour and abilities
During the Mansion Incident, the S.T.A.R.S. encountered Lisa numerous times. The rattling of the chains she wore and her sorrowful moans would warn them of her approach, and due to the stocks she wore she could not walk very quickly. Her arms were bound together by stocks and she would use them to try and club victims to death. None of the S.T.A.R.S. weapons had any effect on her, the years of experimentation by Umbrella hardening her body to resist seemingly any degree of physical impact. During her final showdown with the S.T.A.R.S. in the crypt, Lisa underwent a sudden mutation and several tentacles burst out of her back, increasing her attack range.
Lisa's invulnerability even kept her from killing herself after she recovered her mother's skull. She survived her plummet into the pit and found her way back up to the mansion where she confronted Wesker, one of her old tormentors. Wesker left her crushed under a chandelier before he escaped and the mansion exploded shortly after. Given everything else she has survived, it is feasible that Lisa may even have been able to survive the self-destruct, but she was never encountered again following the Mansion Incident so it is safe to assume that she was indeed killed.