Jack

Jack, code name Raiden, is a Cyborg mercenary currently traveling around the anime universe.

History
Years ago Raiden took part on a mission that sent him to the Big Shell. There he discovered The Patriots, a secret organization that controlled the entire planet from the shadows. Him and Solid snake would quickly team up and destroy the patriots in a massive series of events that is far to large to be summed up here.

Doing this caused Raiden to take up his role in protecting the world from organizations like The Patriots. Its because of him that the normal world has avoided any shadow government type things from being created since.

Years later Big Boss would be reanimated as Bigger boss during the advent of proper Gigaversal travel. This sparked Raiden to follow Bigger boss and make sure he wasn't getting up to any funny business.

Gigaverse Adventures
Upon discovering Grandmother Base during its construction Raiden infiltrated the base in order to assassinate Bigger Boss. However Raiden got fucking annihilated by Bigger boss who used CQC to punch 18 holes into Raidens chest in the blink of an eye.

Raiden would have died right there but at this pivotal moment, out of nowhere, Sheen The Redeemer showed up and rescued Raiden by using the Great Catalysts to warp the both of them to The Trove where Albert Einstein Repaired and greatly improved Raiden's Cyborg Body.