One of the major plot elements of the Resident Evil series is the outbreak of various viruses. These viruses are the creation of the fictional Umbrella Corporation, which is attempting to use them to create Bio Organic Weapons (B.O.W.s).


According to the series timeline, Umbrella Corporation founders Ozwell E. Spencer, Dr. Edward Ashford, and Dr. James Marcus began looking into viral mutation sometime in the middle of the twentieth century with the intent on finding a way to create the perfect biological weapon. This would involve finding or creating a viral agent that could not only be controlled, but could be used to create new bio-weapons by infecting a host organism and mutating it into a powerful creature that could act as a soldier and follow orders, as well as spread the virus that created it into enemy territory. On December 4, 1967, the three men succeeded, with the discovery of the Progenitor virus and from this came the birth of the Umbrella Corporation.

Progenitor virus[]

The Progenitor virus, also known as the Founder or Mother virus, is the first of the mutagenic viruses, and the basis for all of the ones that followed.

According to the series timeline, it was discovered on December 4, 1967, by Dr. Edward Ashford, Dr. James Marcus, and Lord Ozwell E. Spencer. Though Ashford wanted to use the virus' regenerative abilities to help the handicapped, Marcus and Spencer wanted to use it for the bio-weapons project, and after Ashford's death in 1968, they were able to begin their desired research. The only known survivor of an experiment involving Progenitor is Lisa Trevor, who bonded with the virus in a way that baffled everyone involved with the project.

It produces rapid and uncontrollable mutation in a host's genetic code, but the mutations were not coordinated enough to produce effective B.O.W.s. In hosts with a genetic structure less complex than humans, mutations are less pronounced, and usually restricted to increases in size and aggression. In order to enhance the virus's mutagenic properties, Umbrella created a variant of it through synthesizing it with the Ebola virus, but this strain retained Ebola's photosensitivity.


The Tyrant virus, or t-virus, is the main virus used by Umbrella, and is responsible for the creation of most of their B.O.W.s.

According to reports in the game, Dr. James Marcus succeeded in creating the Tyrant virus at the Arklay Management Training Facility on September 19th, 1978[1] through synthesis of the Progenitor virus and leech DNA. Through this synthesis, the photosensitivity of the early Progenitor strain was replaced with pyrosensitivity, a property that can be seen in most of the series' enemies.

The Tyrant virus allegedly operates similarly to most other viruses, but also has the abilities to animate dead tissue, to substantially mutate its host, and to infect nearly any tissue in any type of host. It animates dead tissue by killing and replacing any mitochondria in infected cells, and then combining with these cells to produce enough energy for motor and lower brain functions. By doing this, most of the body's systems, such as the circulatory or respiratory systems, are made redundant. However, this process has the drawback of severe necrosis in the host, and produces the distinctive rotted appearance of most B.O.W.s. The mutations are produced when the virus incorporates itself into the host's genetic code and considerably alters it. Creatures with genetic structures different than humans generally show less severe mutations, and usually only increase in size.

As a side effect of the virus' consumption of its host, specifically its digestion of the host's frontal lobes, all hosts suffer from greatly increased aggression. The virus also damages the hypothalamus, which results in a flood of neurotransmitters, enzymes, and hormones which induce a psychopathic rage and hunger in the host.

The Daylight is the only t-virus vaccine, but must be taken before transformation. The non-canon Live-action film series also present a preventative vaccine known simply as the Anti-virus, which must be taken within several hours after the initial infection. In Resident Evil, it is revealed that if the Anti-virus is taken too late, the t-virus will cause it to be rejected. Umbrella also attempted to develop several other vaccines; t-vaccine was created by WilPharma, but an employee was selling it, as well as t- and G-virus samples, on the black market to bio-terrorists. AT1521 was Umbrella's first official attempt at a vaccine, but the original sample was destroyed. There was also an unnamed vaccine being developed under the Raccoon General Hospital in Resident Evil 3 that was used to save Jill Valentine.

T-Veronica virus[]

The t-Veronica virus is the main virus used in Resident Evil Code: Veronica, and is responsible for the mutation of several enemies. There is also a variant strain of the virus named t-Alexia that is a diluted form of the virus created during its period of cryogenesis in its main host, Alexia Ashford.

According to the series timeline, the t-Veronica virus was created by Alexia Ashford through synthesis of the Progenitor virus and the gene of a queen ant that contained an "ancient virus". She administered it to her father, but because the infection was not controlled, he became unstable and mindless. This led her to discover that the mutations could be controlled if slowly absorbed during cryogenesis.

Like the Progenitor virus and the t-virus, the t-Veronica virus causes rapid mutation, but the infection can be controlled and intelligence can be retained if the virus is absorbed over a long period of time. Alexia Ashford achieved this by remaining in a cryogenic sleep for fifteen years while the virus merged with her at a cellular level. Among the mutations to Alexia caused by the virus were combustible blood and vomit, multiple tentacular muscles, and the ability to exert control over the hive mind of the ants the virus was extracted from.

Though the t-Veronica virus is a useful tool for transhumanism purposes, it is useless as a bio-weapon, as its infection rate is low and it can only be transferred through direct injection. Because she is able to mentally control any organism infected with t-Veronica, Alexia, rather than use the virus as a weapon, planned to use her infected ants to spread the virus around the world by biting and injecting humans and animals with the virus, giving her control of every creature on earth.

NE-T virus[]

The NE-T virus is very similar to the t-virus, but was designed specifically for the Tyrant Project.

According to the series timeline, Umbrella required B.O.W.s that were not only stronger, but could understand and complete missions, and due to the nature of the t-virus, all of its B.O.W.s were unable to do this. The project was divided between an American team, led by Birkin, which would work on increasing the B.O.W.s' strength and ability to detect organisms, and a European team that would work on increasing their intelligence. The two teams traded theories and ideas that included the first experiments in directly operating on a subject's brain. The American team succeeded in creating the NE-T virus, along with the T-002, which could follow simple orders such as "Restrain" and "Attack", though its intelligence was insufficient for field operations.

In response to reports of the T-002’s failure, Umbrella renamed the European team's project with the title "Goddess of Vengeance", or "Nemesis", and gave it the new goal of eliminating all anti-Umbrella elements; specifically, the S.T.A.R.S. The European team made a breakthrough with the creation of the NE-α, an organism created from the NE-t virus that affected the host's brain. Further experiments with this strain led to the creation of the T-103, also known as "Mr. X".

T-Cameron virus[]

The t-Cameron virus is a hypothetical name for Dr. Cameron's experimental "t" strain, appearing in Biohazard 4D Executor. It was created when Cameron injected herself with an experimental serum, to stop the t-virus from spreading when she was infected. However the serum mutated her body, allowing her the capabilities of massive shapeshifting. While her body was killed, another unforeseen side effect of the virus took place when her body was eaten by insects, her consciousness apparently had been encoded within her cells. Given this, she had become effectively immortal, as long as she had a viable host to transfer any source of her corrupt DNA to remake it into her next body. She used these powers to leap from a cockroach that had consumed trace cells from her corpse to a nearby rat, to a crow outside and from there to a member of the U.B.C.S. unit sent to retrieve her investigation. While this last body was destroyed, she had a "backup", which eventually was absorbed by another member of the same unit, allowing her to escape Raccoon.


T-JCCC203 was an experimental t-variant mutagen. It was administered to 63 year old Doug Frost in the Abandoned Hospital during its Drugs, Inc. ownage phase. Doug's cancer was destroyed, but his joy fell short when the t-virus killed him hours later.

The same chemical was administered to 35 year old Dorothy Lester, whose health came back to her to the point she would no longer need a respirator. However the side effect was an increased metabolism, ultimately leading to t-virus infestation and death after she killed an investigator perusing into the Abandoned Hospital's affairs.


The only known successful hosts of the G-virus are William Birkin and Curtis Miller.

According to the series timeline, it was developed by Birkin after its basis was discovered in the mutated body of Lisa Trevor. She had displayed an unexpected immunity to the NE-α parasite that they tested on her, and Birkin and his associates found what would become the G-virus as the cause of this immunity. It turned out that the G-virus was a mutation of the Progenitor virus she had originally been infected with, that arose by absorbing all the other mutagens she had been given. Birkin received approval from Umbrella to begin studying the virus, and completed his work on it in 1998. However, due to disagreements with his superiors, he decided to keep the research to himself and made a deal with the US military to extract him. In response, Umbrella sent in the Umbrella Special Forces Unit to steal his research and virus samples. The unit shot Birkin and left him for dead, but while dying, he injected himself with a sample of the virus, and mutated. He tracked the USS team to the sewers, and during the ensuing onslaught, several t-virus vials were dropped and broken, causing the city-wide infection, spread through rodents. However, HUNK, the lone survivor of the team, was able to escape and deliver the virus to Umbrella. It was later discovered by Claire Redfield that the pharmaceutical company "Wilpharma Corporation" had purchased a sample of the virus on the black market, with the intent to develop a vaccine. These plans, however, were soon dropped. Soon after, Curtis Miller, a survivor of the Raccoon City incident, demanding that the world know the truth about the outbreak, along with the government's involvement , injected himself with a sample of the virus, mutating himself before eventually being killed falling from a high height in Wilpharma's research dome, after unsuccessfully trying to obtain his sister, Angela Miller, to pass on the G-virus. Members of the Tricell company later began to salvage Curtis's remains, for reasons as of yet unknown.

The mutations induced by the G-virus tend to be extremely volatile. Unlike the t-virus, the mutations caused by the G-virus occur much faster, and continue as long as the host is active, even lacking external stimuli, though they are more rapid and substantial when the host is wounded. Also, the G-virus possesses none of the necrotizing properties that the t-virus is known for. The virus is transmitted through implantation or ingestion, rather than physical contact. It can only be accepted fully by hosts with a suitable genetic makeup, specifically a blood relative. However, it can also partially infect others by implantation of G-embryos, producing severe mutations that culminate in the host being able to release further G-embryos. Hosts, called G-mutants, create their offspring by orally implanting small, parasitic organisms into a living host through the palm of their hand. If the host is compatible, the embryo begins to pupate and assimilate the host's body, turning them into a mutant of immense strength. If the host is incompatible, the embryo will rapidly grow inside the host's body, and will burst from their chest in a matter of minutes. They will then quickly mutate into their adult form and search for another host.

Though the G-virus is a somewhat useful tool for transhumanism purposes, it is inefficient as a bio-weapon, due to its poor communicability.

The G-virus can be cured by DEVIL, an experimental vaccine. However, the vaccine is only effective during the initial stages of an impregnation-induced infection, before the embryos gestate.

Other viruses[]

Unknown virus[]

In Wesker's Report, it is revealed that Birkin gave Wesker an unnamed virus to use when he faked his death in 1998 at the Mansion Incident, and as a side-effect he receives superhuman strength and speed. It has no visible side-effects besides changing the color of his eyes. According to CAPCOM's Resident Evil website, the virus is a version of the t-virus.[2]

The virus speeds the host's metabolism, giving it heightened strength, speed, and regenerative abilities. Unlike the other viruses featured in the series, it is not a severely mutagenic virus, and its effects are limited to muscle tissue and lower organs, leaving the nervous system untouched.

As a prerequisite to increasing the host's speed, the virus also affects ocular tissue, allowing it to view and process visual information at a speed allegedly equatable to raptors. This modification of the eyes is the only visible effect of the virus on its host.

The virus is discussed in one of the files of Resident Evil: The Umbrella Chronicles. This file, called "Memo about Virus", explains that the virus is from the "mutation stocks". Requiring an injection of at least 5 minutes prior to use, 10% of subjects fail to revive, while 20% revive as they were originally and 70% revive with its beneficial mutations to the muscle system and circulatory system.


The tG-virus (also known as Reagent 92), as its name suggests, a fusion of the t and G-viruses. It imbues its carriers with qualities of both strains, as well as odd electrical properties. As demonstrated by Morpheus Duvall, it causes instant mutations when injected into a human host.



  1. September 19th: At last...I've discovered a way to build a new virus type with Progenitor as a base. Mixing it with leech DNA was the breakthrough I needed... I call this new virus t, for "tyrant".
  2. Resident Evil 5 Characters - Wesker: "Wesker encountered Chris Redfield again at an underground laboratory in Antarctica, but the superhuman abilities Wesker had gained from exposure to the T-virus meant Chris could barely hold his own in the fight."