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Prime universe
(Capcom's primary storyline)
Uroboros vial - revelations 2

Uroboros vial that Alex Wesker injected herself with.

"Uroboros will be released into the atmosphere ensuring complete global saturation."
— Albert Wesker[1]

Uroboros (ウロボロス?) is an RNA virus in the Progenitor family. It was engineered in the 21st century by Dr. Albert Wesker as the ultimate eugenics tool. Later, a less potent strain was developed by Dr. Alex Wesker to serve as a bio-weapon. Currently, there is no known vaccine for either strain of Uroboros. The virus is named after the Ouroboros in Greek mythology, which is a snake or snake-like creature that consumed itself.[2]


Work began on the Uroboros Project sometime in 2006, following an encounter Dr. Albert Wesker had with Dr. Oswell E. Spencer, Earl Spencer, who revealed to him Umbrella Pharmaceuticals' secret eugenics goal of creating a race of Übermensch to advance human society, with Wesker himself being part of such a project.[3] Having begun to question the emerging War on Terror, he concluded that humanity itself was the problem, and the only way to bring about a utopian society of the Übermensch was to use the Progenitor Virus against the very planet itself, which would kill all but those with certain genetic characteristics. Such people would theoretically be enhanced physically and mentally.

The first setback took place after Tricell, Wesker's partner, set up a lab in the old Ndipaya Kingdom. The human population ratio able to survive and mutate from Progenitor infection was simply too small. Using t-Virus antibodies extracted from a mutant test subject, Jill Valentine, Wesker repeatedly used them on his Uroboros cultures to naturally select a new strain distinct and less potent than Progenitor.[4] With a virus now useful in research, the project moved to its next stage and saw thousands of other test subjects infected over the next two years, with increasing assistance from Tricell's own research staff such as Miguel. The virus was more or less finalized by May 2008 when samples were loaded onto missiles in preparation for the final stage in the "Uroboros Project" - dispersing the virus across the Earth's atmosphere to infect every corner of the planet. There were problems with the preparations, however, and a fire occurred, resulting in the creation of a mutant arthropod species dubbed "Reaper".[5] In March 2009, the project was finally underway, but was stopped by the Bioterrorism Security Assessment Alliance. At least four humans were infected with Uroboros during the operation, including Wesker himself. Only he mutated appropriately, however, with the other three being genetically incompatible. In their case, their bodies were torn apart by uncontrollable mutation, and in one case, consumed a number of other bodies.

Continued research[]

"Uroboros... It's not death... it's power!"
— Neil Fisher while mutating

Sometime after Albert Wesker's death, his compatriot Alex Wesker managed to obtain a sample of Uroboros. She took it to Sein Island, where bio-weapons research began shortly after the work on the t-Phobos Virus was completed.[6] The injection of Uroboros into the corpses of failed t-Phobos test subjects resulted in the creation of the Revenant.[7]

In 2011, Alex Wesker conspired with TerraSave leader Neil Fisher to provide Uroboros in exchange for more t-Phobos test subjects. However, Fisher was infected with the virus instead of being handed a sample, as punishment for betraying his friends.

Upon her own mutation from Uroboros and t-Phobos, Alex released her Revenants from the laboratories and let them loose across the island. Over the next six months, they slowly consumed every last food source, from corpses to wildlife. They were eventually eradicated by a BSAA team.

During the time when Barry Burton, Claire Redfield, and Moira Burton (Barry's daughter, who had been kidnapped) confronted a horrifically mutated Alex Wesker, and severely damaged her. She consumed large doses of Uroboros, augmenting her and making her enormous in size. At the end, Claire destroyed Alex by firing an RPG right into her exposed heart, ending her life, experiments, and reign of terror.

Viral disease[]

Comparable to the Progenitor virus, the Uroboros disease is noted to be almost always lethal in humans, with the exception of those with a particular genetic trait shared with the Ndipaya King. The disease goes through two stages, which can be defined as early and later symptomatic stages.

In the early symptomatic stage, patients are known to experience sweating, labored breathing, and confusion or delirium. The Uroboros Project research team noted in their findings that the onset of symptoms appeared immediately after infection. However, it should be noted that patients in the lab trial were each infected with massive viral loads, equating to one vial for people over 60 kg and two-thirds for those at 40–60 kg.[8]

In the later stage of infection, the patient's condition will develop in one of two ways. If the patient has the advantageous genetic trait, the virus will enter a lysogenic stage and mutate the host at a slow rate. Patients without this trait, however, will experience runaway mutations that result in the patient being violently torn apart and killed. The infected biomatter continues to endure as its own separate entity, known only as "Uroboros".[8]

Like the Progenitor and Golgotha viruses, Uroboros is able to repair dead cells and revive the dead, which results in Zombies who demonstrate neither superhuman abilities nor become typical Uroboros. The extent of Tricell's research into Uroboros Zombies is limited, however, and should be noted.

Uroboros creature biology[]

From a biological standpoint, Uroboros creatures can be described as anomalous masses of black biomatter. This mass often has tubular characteristics, echoing its namesake, though rather than resembling a snake, these creatures' tubules branch off from one another like tree roots, and can be melded back into the mass to grow elsewhere. When an Uroboros creature makes contact with other organisms, it consumes and converts them into biomatter for its own growth. As seen in the case of Uroboros Aheri, these creatures can reach several stories in height if exposed to a large food source.[8] Due to the simplistic and amorphous nature of Uroboros creatures, only one organ has been identified in them, which resembles a yellow cyst. This organ takes on the roles of both a sensory organ and a brain of limited intelligence, allowing the creatures to identify and attack nearby human prey.[8]

Following Tricell's work, Dr. Alex Wesker also undertook research on Uroboros, looking at it for its bioweapons applications. A variety of creatures were produced from this research, which maintained the forms they were created from rather than assimilating biomass. One of the more extreme examples of this research is that of the Revenant. Inspired by The Creature of Mary Shelley's Modern Prometheus, these were not zombies brought back to life, but the product of random body parts stitched together and operating as a single entity controlled by a yellow cyst rather than its actual brain.

Known Infectees[]


Further notes[]

  • Although never referred to as such in dialogue, two of the three Uroboros creatures fought in-game have specific names: The one created in the laboratory was called Uroboros Mkono, and the one "birthed" from Excella Gionne was called Uroboros Aheri.
  • It is unknown if Albert Wesker's mutation is consistent with his expectations. As a mutant, he was already genetically distinct from the population the virus was intended to infect. Neil Fisher was also infected with the t-Phobos Virus,[9] which may explain his own unusual mutation, though this was a separate Uroboros strain.
  • In a trailer for the rejected "Castle" version of Resident Evil 4, Leon is seen fighting a black tentacle mass that bears a similarity to Uroboros.[10] The creature is officially dubbed as "Black Fog" by the developers. In the story, it was created by Albert Wesker (said to be a combination of multiple viruses) and released by his special forces team, known as the H.C.F.
  • The trailer for the non-canonical Wesker Mode for the HD Remaster of Resident Evil 0 mentioned Uroboros, where it implied that Wesker was empowered by the Uroboros virus during the spin-off game mode.


  1. Resident Evil 5 (2009), scene: "Sky-high Skirmish".
  2. Resident Evil 5 (2009), file: "Uroboros Plan".
  3. Resident Evil 5 (2009), file: "Albert Wesker".
  4. Resident Evil 5 (2009), file: "Jill Valentine".
  5. Resident Evil 5 (2009), file: "Regarding the Mutant Organism Found in the Facilities"
  6. Resident Evil: Revelations 2 (2015), file: "Research Facility Chief's Journal 2"
  7. Resident Evil: Revelations 2 (2015), file: "Researcher's Journal".
  8. 8.0 8.1 8.2 8.3 Resident Evil 5 (2009), file: "Directions for use of Uroboros Virus".
  9. Resident Evil: Revelations 2 (2015), file: "Neil's Candidate List".
  10. Biohazard 4 "Castle Version" TGS 2002 Trailer