The Umbrella Corporation is a biological engineering megacorp company, which as we all know emerged within the Resident Evil video games..... In the video games, it is a major international player in a number of markets including pharmaceuticals, medical hardware, defence, and computers along with more clandestine operations utilizing genetic engineering and bio weapons. The company also has a more public face, producing cosmetics and consumer products.

The T-Virus is essentially a protein crystal with a RNA core. Once the virus makes contact with a cell it is able to infiltrate the nucleus, and manipulate the cell's DNA. The T-Virus becomes an essential part of the cell, and as the cell replicates, the virus is copied with each division. The virus will gradually destroy a cell's mitochondira, and replace it with a special organelle which produces a new-found form of energy. As the body becomes self sufficient on this energy, the respiratory and circulatory systems will become vestigial, ending the body's dependence on oxygen.

By manipulating the virus' genetic structure, Dr. James Marcus was able to alter the regeneration process so that it is dependant on the host's body sacrificing its own cells. This "degeneration" will lead to the deformation of the host. The host of the virus doesn't need to be deceased at the time of infection. If the host is alive during the time of infection, its frontal lobes will slowly deteriorate, insidiously deprecating one’s higher thought process. Primitive thought structures will soon take control of the body, resulting in irrational and animalistic behavior. Symptoms of infection include: painful skin irritation, insatiable hunger, and spontaneous antipathy towards people or objects.

If the host is subdued after the virus is able to take control of the body, it will enter a dormant state. During this period, the host's body will metamorphosize, creating rejuvenation within the muscular and skeletal features. The metamorphosis will also force blood to evacuate through the pores, which is complemented by the growth of deadlier claws and teeth. Known as "V-ACTs", these creatures possess incredible destructive capabilities, and once killed, will not regenerate. Incinerating or decapitating the corpse of a slain carrier can prevent metamorphosis.