"G" is the name given to any mutant created through Golgotha, whether as the Patient Zero or their descendants. For convenience, only these descendent will be referred to as "G" here. These "G"s come in two varieties. The first is the immediate offspring of the Patient Zero, which mature from embryos into tumour-scarred humanoid forms if rejected by a human parasitic host. The second is their own descendants, which remain in embryonic form and cannot develop further.
The only known occurrence of Gs was during the Raccoon City Destruction Incident that took place in September 1998. Monica, a researcher on the G-Virus R&D Team, was parasitised by a G-embryo that crawled down her throat when she was attacked by a Giant Moth in the Raccoon City Underground Laboratory. Not genetically compatible, it rejected Monica and tore out of her chest. The creature matured into its adult form within minutes, but was soon killed by a group of survives on the surface.
Dr. William Birkin, who infected himself with the virus after being shot, hunted for human hosts to carry his embryos. The only confirmed parasitism was that of his own daughter, Sherry, who was a genetic match. Though he also interacted with Brian Irons and Ben Bertolucci, among presumably others, it is not known if he parasitised them or simply killed them.