Unlike the T-virus the G-virus would attack the host at the cellular level causing unlimited mutations and the ability to reproduce with those that have a genetic match. William Birkin injected himself with the G-virus after being shot, the result is the creature known as G.

G underwent many mutations, the first of which was the mutation of Birkin’s right arm. It remained human in appearance but the arm now had a giant functional eye. The arm became a monstrous limb, giving it super strength. All sense of reason and emotion left Birkin once he became G, the only thing the creature wanted was to reproduce, and thus G needed Sherry. Leon and Claire came into contact with G many times as they tried to protect Sherry from it.

The second version of G remained expanded on the eye and right arm, giving it larger claws. This time Birkin’s head sunk into his chest and a new head emerged. Slowly G was becoming less human and more of an abomination of science.

The third form of G grew two new arms and its old ones became wing-like in shape with massive claws. It grew another eye on its thigh and a sort of mouth on its chest. This form of G attacked the survivors on a tram that lead to the underground Umbrella lab.

As Leon and Claire were escaping the base the third form of G attacked again. When it was close to death it underwent another mutation bringing about the fourth form. This form became animal like, moving on all fours, with a giant mouth filled with sharp teeth. Now it had much more mobility but its constant mutations demanded more energy, ergo, it needed to feed more often. The insatiable feeding led to more and more mutations.

The fifth form became a massive blob of flesh and teeth. It grew huge tentacles, which it used to practically absorb things into its skin tissue. This form took residence inside the escape train Leon, Claire and Sherry were riding. The only way to destroy the monster was to blow up the train along with G on it. The survivors jumped off the train as it exploded ending the G’s life. What kind of monster would G have turned into if it was allowed to mutate further?