How did Wesker get the G virus?
Shortly before leaving with the S.T.A.R.S Alpha Team, Birkin gave Wesker a syringe containing a virus. After using it to fake his death at the hands of the T-002 Tyrant, he escaped the underground facility, becoming a Metahuman.
With the Uroboros Virus, Wesker would have a new organ on his chest and his upper body would become wrapped in various tentacles. Thanks to these viruses, Wesker would receive advanced genetics that made him more "superior" than most humans.
However, his plan was ruined after the Tyrant was destroyed by his former subordinates, and he survived his apparent death in the first game by injecting himself beforehand with an experimental variant of the T-virus, provided by his former Umbrella colleague William Birkin, that revived and augmented him with ...
Spence and Alice remember that Spence was the thief who stole and purposefully released the T-virus, and hid the T-virus and anti-virus on the train.
As a result, Uroboros became an extremely lethal virus that bestows its survivors with superhuman abilities. Uroboros does this by "forcing" its infected to "evolve," therefore it could only become compatible with a certain population.
t-Phobos was engineered by Dr. Alex Wesker to trigger mutations in humans when it came into contact with certain levels of stress hormones indicative of fear. C-Virus was a heavily re-engineered strain of t+Veronica used by Neo-Umbrella in 2012 for bioterror purposes.
Jake is the biological son of series villain Albert Wesker.
The Golgotha Virus, abbreviated as G-Virus, is a retrovirus in the Progenitor family of viruses. Golgotha was developed by Umbrella USA as a bioweapon to rival and surpass Tyrant Virus ("t-Virus").
Albert Wesker reached a biological state that could be considered the next stage in human evolution as a result of his infection with a unique variant strain of the t-Virus.
The once invincible, bullet-dodging Wesker deliberately infects himself with the Uroboros virus as a last resort after having been weakened by an overdose of the virus suppressant PG67A/W that was injected by Chris and Sheva.
Why is Wesker so strong?
Powers and Abilities
Superhuman Strength: Thanks to his injecting himself with that prototype virus, Wesker's strength is so much that he can throw large missiles with one hand, lift steel girders off his body, and kill a B.O.W. with one strike.
As a clone, Albert underwent rapid aging, progressing from age 0 to 20 in less than six months. That sort of rapid cell growth causes all sorts of nasty problems and complications, including cancer and tons of other things. Albert gets sick and weak from time to time and that's when he injects himself with the blood.
The G-Virus, or the Golgotha Virus, was harvested and created by by Dr. William Birkin in the Umbrella facility below Raccoon City in 1988. Upon discovery, it was intended to rival the T-Virus, and produce a more intelligent, powerful and controllable bio-weapon.
Seeing the eugenics potential of a virus capable of mutating humans into a superior subspecies, Birkin sought funding from Umbrella HQ to allow him to work on "Golgotha", known in shorthand as the "G-Virus".
In Resident Evil 2, a vial of T-Virus gets spilled on the floor when a group of Umbrella agents almost kill Dr. William Birkin. This results in some rats getting infected, spreading the virus through Racoon City's sewers, and eventually leads to the widespread zombie outbreak.