The 'T-virus', which stands for 'Tyrant-virus', is an RNA virus developed by the international pharmaceutical company Umbrella. It was created for use in the development of 'Human biological weapons', better known as zombies. By using it to mutate a victim's genes while also adding the DNA of an amphibian, the 'Fighting biological weapon', known as the Hunter, was also created. An even deadlier 'Fighting biological weapon', called the Tyrant, can be made by injecting the 'T-virus' into a perfectly compatible host.