The Tyrant virus, more commonly known as the "T-virus" or "t-Virus", is the second mutagenic virus discovered by the founders of the Umbrella Chemical, inc.. While the T-virus is responsible for the creation of the majority of their Bio-Organic Weapons (or B.O.W.s), the original intent was to create the perfect B.O.W.: the Tyrant.
Midway through the twentieth century, the Progenitor virus (also known as the Mother virus) was discovered by Lord Ozwell E. Spencer, Sir Edward Ashford, and James Marcus. These three gentlemen had a certain economic position and decided to begin research upon the virus. Most of the research was carried out by Marcus, as Ashford died in 1968 and Spencer was already occupied by his burgeoning chemical corporation, Umbrella. Marcus had little resources to pool into the investigation, until Spencer agreed to employ him as a researcher and later Director of his Corporation's Training facility, putting the vast resources of Umbrella into his hands.
Marcus overbid his hand, greedy for the power to finally invest serious amounts into his research, demanded numerous resources to perfect and improve what he envisioned was his life's work. This led to friction between Marcus and Spencer who, to compensate from the crippling economic demands laid by Marcus, demanded that he create a virus with a 100% effectiveness rate, much to the confusion of Marcus and his assistants, new Umbrella Trainees Albert Wesker and William Birkin.
The Umbrella Corporation used its finances to secretly develop the virus under the radar of international authorities. In time, Marcus further evolved the virus, creating the first effective bio-weapon to be produced in large quantity and be closely studied by the Umbrella Corporation. By adding the virus to leeches, the attributes of both were combined, and the T-virus soon saw the light circa 1978.
Though most of the research for the virus took place within the Arklay Laboratory underneath the Spencer estate near Raccoon City and the Umbrella Training facility under Marcus' orders, covered by the American Umbrella offices, Spencer's Umbrella empire in Europe raced against Marcus to adequate the T-virus to create a virus with an even greater destructiveness. Marcus' dreams to overthrow Spencer and his attitude towards the virus as a "money-spinning tool" for Umbrella were never fulfilled, as he was murdered before he could enact them. Birkin came to be known within Umbrella circles as the true creator of the T-virus. During those years, vast numbers of t-Viral strains were developed in the Arklay Laboratory, and tested upon one solitary test subject: Lisa Trevor. For years, she was subject to intense biological torture, which, despite all odds, she survived.
As well, William Birkin, grown conceited as being credited as the creator of the T-virus, spawned a myriad of biological weapons to serve as backup to the virus, to ensure a 100% death ratio in any populace the virus should be released. Among these are the Hunters (created by fusion of a human fertilized egg with T-virus infected reptilian DNA), the Ivies (flowers grown to unnatural proportions and given animal instincts, locomotion and rudimentary defence mechanisms), the Chimeras (a mixture between a fly and human given vague humanoid appearance, increased size and mass, improved claws, and better reflexes), the Cerberus' (infected dogs), and most importantly, the crowning achievement of Birkin's career for the time: the Tyrants.
Later, Lisa Trevor's body, by now a melting pot of unthinkable disease, had deteriorated to inhuman levels. Noting she was, while not a Zombie, incredibly stronger, slightly more intelligent, and impervious to all damage, Birkin decided to test the NE-α Parasite (by then reputed to kill all its hosts, no matter how strong, in a matter of twenty minutes) in her. The results astounded even Birkin: Lisa's body, by then a hideous amalgam of all viruses ever tested on her, overcame the parasite and absorbed its rejuvenation properties, giving her even more destructive capabilities, greater strength, and total invulnerability to gunfire. Even with shackles she could not be bound, so after she outlived her capacity when Birkin extracted what would become the G-virus deep from her, he had her killed and disposed of.
When the time came, in early-1998, James Marcus revived, rejuvenated by the immense power of the first T-virus strains, coordinated into a steady pace by his own DNA and that of his leeches. For more than three decades, the T-virus threat had been averted, but at the time of his awakening, the Arklay woodland slowly was corrupted by the infectious agent. Before long, the Arklay laboratories had fallen; as the former Umbrella Training Facility was thought deserted, an Umbrella team (likely to be the U.B.C.S.) was dispatched to destroy the infection from there, before Marcus wiped out the entire platoon with his army of leeches.
From there, stories started stemming from the forest; several killings took place and an elite team of paramilitary units, the S.T.A.R.S. Bravo team, was sent from Raccoon City to destroy the threat, oblivious to its real cause. Only four of these members, Rebecca Chambers, Enrico Marini, Kenneth J. Sullivan, and Richard Aiken survived the night. All of them ended up holed up in the massive Spencer Estate and its adjacent areas, where later the S.T.A.R.S. Alpha team entered as well, after suffering a similar fate at the hands of a pack of Cerberus'.
Later on, the remaining members of S.T.A.R.S. met up at the underground laboratory where the Tyrant T-002 was kept. This Tyrant killed, albeit temporarily, Albert Wesker, and was destroyed by a rocket blast in the second brawl it offered the remaining S.T.A.R.S..
After the demolition of the manor, the virus sources were thought stopped definitively, but when William Birkin's subterranean laboratories were attacked by Umbrella's Black Ops in September 1998 in an effort to retrieve his G-virus, another outbreak ensued. This infection encompassed all of Raccoon and ended in the forced termination of the entire city. Umbrella was immediately exposed as creator of the virus due to the enormous amount of evidence produced from the scarce survivors, and was shut down.
Still, another outbreak was induced in late 1998, on Rock Fort Island, this time by the revived Albert Wesker and his new organization, the Agency. This ended in the partial demolition of the Umbrella installations there and the total destruction of the South Pole Umbrella Research Center.
Yet another occurring on Sheena Island; an Umbrella owned Tyrant Factory. Hundreds of people from across the globe were kidnapped and taken there to be made into Tyrants. This infection was caused by the - now mad with power - Commander Vincent Goldman. The island was "sterilized."
Another occurred on an Umbrella-owned luxury cruiser, the Spencer Rain caused by an ex-Umbrella terrorist. All crew and passengers were transformed into Zombies with the virus.The ship was destroyed when it crashed into an island which housed the -also infected- Umbrella Atlantic Facility, and a secret underwater Missile Silo.
The last known outbreak occurred in 2005, within the Harvardville Airport, where the infection began after a single zombie entered the building and began to attack people within the building. A small-scale outbreak happened at the nearby WilPharma Corporation bio-dome facility, after a bomb was detonated. Both facilities were eventually sterilized, however.
No matter how many outbreaks have been halted, the T-virus remains a constant threat to global safety.