A disturbing virus discovered by William Birkin inside the body of T-Virus test subject Lisa Trevor. The virus induces multiple spontaneous mutations until the host itself perishes.

Unlike the T-Virus which can only affect a single generation, the G-Creatures that result from G-Virus infection are capable of reproduction, which can eventually result in the creation of entirely new life forms. It is also thought the G-Virus has the ability to resurrect the dead.