(Capcom's primary storyline)
"Uroboros will be released into the atmosphere, ensuring complete global saturation!"
Uroboros was an RNA-based virus derived from Progenitor. It was engineered by bioterrorist Albert Wesker, who received significant funding from Excella Gionne, CEO of TRICELL, Inc.'s African division. The virus is known to have gone through three stages of development - two overseen by Albert Wesker himself, and a third by Alex Wesker.
Albert Wesker was raised since his very childhood into believing in Oswell E. Spencer's view of the world, where the strong dominated the weak. Consequently, he grew up to be a vehement proponent of the eugenics movement. Whereas Spencer's own "Project W" aimed to create a superior race of human beings to dominate all others, Wesker instead wished for the inferior humans to be destroyed, leaving behind only the worthy.
With the collapse of Umbrella following the 2003 Raccoon Trials verdict, elements of Tricell linked to the emerging bio-weapons black market became interested in reclaiming the corporation's data for their own purposes. Albert Wesker, a former Umbrella researcher and millionaire black market dealer, reached an agreement with Tricell's Excella Gionne and Ricardo Irving to aid them in bio-weapons research in exchange for funding for Uroboros. In order to create the virus, an unaltered strain of Progenitor was needed. For this, Tricell tracked down Umbrella's African Research Center.
In 2006, a prototype version of Uroboros was created. A problem was quickly discovered in the virus: it was too potent. Rather than save Wesker's chosen "worthy" from death as expected, infection was fatal for everyone. A solution was found in the body of a test subject, Jill Valentine, who had antibodies for the t-Virus. For helping put Uroboros back in development, Jill Valentine was kept alive and did not take part in the virus trials.
Perfected Uroboros strain
The modified Uroboros continued to be developed over the next few years, with increasing assistance from Tricell's own research staff such as Miguel. The virus was more-or-less finalised by May 2008, when samples were loaded onto missiles in preparation for the final stage in the "Uroboros Plan" - 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. Fortunately for the research staff, an irregular mutant called "Reaper" was created in the accident.
The following year a series of leaks took place alongside the execution of the Tricell research staff. This was part of a plan to drag the BSAA into the Kijuju Autonomous Zone, the testing bed for Tricell's Type 2 Plagas, and eliminate the only threat to the Uroboros Plan. Thanks to a spy by the name of Reynard Fisher and data obtained by the BSAA Alpha Team before their deaths, agents Chris Redfield and Sheva Alomar soon discovered the plan and were able to track down and kill Albert Wesker before he could disperse the virus.
Sometime after Albert Wesker's death, his compatriot Alex Wesker managed to obtain a sample of Uroboros. Taking it to Sushestvovanie Island, bio-weapons research began shortly after work on the t-Phobos Virus was completed. The injection of Uroboros into the corpses of failed t-Phobos test subjects resulted in the Revenant. In 2011, Alex Wesker conspired with TerraSave leader Neil Fisher to provide Uroboros in exchange for more t-Phobos test subjects. Neil was instead infected with the virus rather than handed a sample, Wesker's punishment for him betraying his friends. Upon her own mutation from t-Phobos, Alex released her Revenants from the laboratories and 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 both Barry Burton and Claire Redfield along with Moira, Barry's daughter who been kidnapped, confronted horrifically mutated Alex Wesker, and severely damaged her, she consumed large doses of Uroboros, augumenting her and making her enormous in size. At the end, Claire destroyed Alex by firing an RPG right into her exposed heart, ending her experiments and reign of terror.
In its original form, Uroboros was too deadly for any host to support life. Only with the introduction of Jill Valentine's t-Virus antibodies could Uroboros' rapid amplification be controlled so that it left a select percentage of the human population alive.
Once Uroboros comes into contact with an organism's cells and infects them, it inserts its genes into the host's genome in an attempt to merge with the host. For those whose genetic sequence is compatible with Uroboros, the merge is successful, bestowing superhuman abilities upon the host. Those whose genomes are incompatible fall to the virus' uncontrolled amplification, and their cells are overtaken by Uroboros. The resulting infected tissues, organized into undifferentiated tentacles, absorbs the body of the host and any other organic matter it can reach. These tentacles are held together by orange pustule-like organs, which serve as the control center of the organic growth. Destruction of the core negates the body's cohesion, and thus, life. The same happens when the virus is injected in any corpse.
When a human host successfully adapts to the virus, they retain their normal human form but become superhuman with increased strength, speed, durability, vitality and a strong regeneration ability. The only physical sign of mutation in an adapted host is the appearance of glowing slitted eyes, similar to those of a host successfully adapted to the Progenitor virus or the prototype t-virus variant Albert Wesker adapted to. However, due to its purpose of forced evolution, it was designed to accept a small percentage of the human population possessing excellent genes. If Uroboros had been spread across the globe, it would have killed those with unsuitable DNA and selected for genomes containing genes favorable to evolution.
Uroboros was sensitive to intense heat as shown in all encounters with Uroboros, also after Wesker's bonding with Uroboros and falling into the lava he was unable to attack Chris and Sheva, only being able to launch one of his arms at the helicopter Josh piloted. The heat generally comes from places like furnaces and lava pits, although any heat source could work, as evidenced by Neil Fisher's Uroboros-infected form being vulnerable to the heat generated by a flashlight.
Not much else can be said without extrapolating information, since there have been only five hosts seen in the games, three of which were incompatible. Because Wesker's situation, with his preexisting virus and possibly the overdose on PG67A/W, is so unique, it is difficult to say if the symptoms he showed were typical of all compatible hosts, or if they were peculiar to him, though saying Wesker is typical is not the best description (he might have been bonding, but was killed before it completed). It is possible that Uroboros-infected cells, with or without a compatible host, develop a form of sentience, or at least characteristics of an individual organism. The effects shown by Wesker was the ability to use electricity with the metal he picked up (although it might be because of friction), and he had increased jumping ability with increased resistance of damage, regeneration, and strength (although he was overdosed with PG67A/W which made him weaker and poisoned from the inside).
- 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 Wesker's theory was true of the Uroboros being the Philosopher's Stone by selecting humans that are "worthy" enough to survive the merging process as there are currently no other human that had survived being merged by the Uroboros aside from Wesker himself, although he might have gained immunity from the Uroboros through the Prototype-virus that Birkin gave him which granted him his powers. In Resident Evil Revelations 2 this theory is explored further as Neil Fisher also seems to have survived the merging process as well, retaining most of his awareness and becoming a very powerful being. Albeit not retaining his regular human form like Albert Wesker, his changes were much more severe, However this theory can be counteracted as Neil was also infected with an inactive form of T-phobos at the time, given the activation of T-phobos being exposed to large amounts of fear. It's possible that Neil was the product of both viruses being used at the same time, similar to Albert Wesker, so at this point it is unclear what exactly a pure human being unaffected by other viruses would actually look like after infection.
- In a trailer for the rejected 'Castle' version of Resident Evil 4, Leon is seen fighting a black tentacle mass which bears a similarity to Uroboros. 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 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.
- Uroboros is likely named after Ouroboros, a mythical serpent (or dragon) that devours its own tail. The ouroboros often symbolizes self-reflexivity, introspection, or cyclicality, especially in the sense of something constantly re-creating itself, the eternal return.
- ↑ Resident Evil 5 (2009), file: "Albert Wesker".
- ↑ Resident Evil 5 (2009), file: "Uroboros Plan".
- ↑ Resident Evil 5 (2009), file: "Jill Valentine".
- ↑ Resident Evil 5 (2009), file: "Regarding the Mutant Organism Found in the Facilities"
- ↑ Resident Evil: Revelations 2 (2015), file: "Research Facility Chief's Journal 2"
- ↑ Resident Evil: Revelations 2 (2015), file: "Researcher's Journal".
- ↑ Resident Evil 4 prototype