In 1966, Western scholars Edward Ashford, James Marcus and Oswell E. Spencer discovered the Progenitor virus and attempted to cultivate it themselves. Their initial attempts all failed as something about the Stairway to the Sun's environment contributed to the production of the virus, meaning that cultivation could only take place in the flowers' native soil. In the years that followed, Spencer, Ashford and Marcus founded the Umbrella Corporation as a front for their research into Progenitor; while Marcus conducted his research into the virus, Umbrella would develop and market new medical products and technologies which would fund their more illicit work: developing Progenitor as a biological weapon.
In 1978, Marcus would reach a breakthrough in his research after combining Progenitor with leech DNA. This combination resulted in the creation of a new virus that Marcus dubbed "Tyrant", or "T". While Progenitor itself proved to be ineffective as a bio-weapon in and of itself, it nonetheless proved to be instrumental in the development of effective, marketable viral agents for decades to come.
The Progenitor virus has lain at the centre of virtually all bio-weapons development in the Resident Evil series. Though it has never been utilised as a weapon in its pure form, it has provided the groundwork for the creation of just about every viral agent throughout the series. The viruses derived from Progenitor are listed below.
- T-Virus - The first and most well-known of all the Progenitor-based mutagens, the Tyrant virus was originally created by Umbrella co-founder James Marcus when he combined Progenitor with leech DNA. Since its creation, the T-Virus has led to the development of many types of B.O.W., most notably the Hunter and Tyrant series. Its most noteworthy aspect is its ability to reanimate the bodies of deceased human hosts as cannibalistic zombies. It has also been the cause of several biohazardous disasters, the most infamous of which is the Raccoon City Destruction Incident.
- T-Veronica - Created by child prodigy Alexia Ashford, the T-Veronica virus was developed by combining the Progenitor virus with select gene sequences found in certain plants and queen ants. Alexia's intent was to develop a virus that would allow the host to retain their intellect after infection, allowing the host to utilise the power of the virus to its fullest potential. To this end, she injected herself with the virus and had herself cryogenically frozen to allow her body to fully adapt to it.
- G-Virus - This highly unstable mutagen was developed by Umbrella researcher William Birkin. This virus was discovered in 1988 within the body of longtime test subject Lisa Trevor, who had been injected with multiple viral agents over her years of confinement. This viral cocktail, when introduced to an NE-α parasite, resulted in an extremely potent mutagen that rapidly and constantly regenerated living tissue, resulting in the frequent transformation of its host.
- T-Abyss - A mutagenic virus that was created by combining a marine virus known as "Abyss" with the T-Virus. This virus was developed by scientists at Montpellier Marine University and the mutations that stemmed from it were predominantly aquatic in nature. T-Abyss was used during the Terragrigia Panic of 2004.
- Uroboros - The deadliest variation of Progenitor ever conceived, Uroboros was created by former Umbrella scientist and terrorist Albert Wesker. The purpose of this virus was to bring about the evolution of the human race by enforcing natural selection; only a handful of humans possessing specific DNA types would survive infection and be transformed into superhuman beings whereas the rest of humanity would be killed off. Wesker attempted to release Uroboros into the Earth's atmosphere and saturate the entire planet, but his plan was foiled by BSAA agents Chris Redfield and Sheva Alomar.
- T-Phobos - A derivative of the T-Virus created by Alex Wesker. Considered to be a less lethal version of T, this virus would only be triggered by the emotional responses of its host. If a host experienced a state of panic, they would undergo a sudden and violent mutation, becoming Afflicted.
- C-Virus - The Chrysalid virus was developed by virologist Carla Radames by combining enhanced strains of the G-Virus and T-Veronica virus. Humans infected with this agent were transformed into B.O.W.'s known as J'avo that would undergo extreme mutations in response to injury. A gaseous variant of C also transformed human victims into zombies similar to those created by the T-Virus. C was deployed by the terrorist group Neo-Umbrella in a series of attacks in 2013.