You may be looking for:
Marcus Wright was a marine aboard the Grey Tiger. He was six-and-a-half feet tall and weighed about 100 kilograms. A scar reached from his chin to his temple. He was cheerful, due to the neural resocialization he had undergone and had a gravelly voice due to smoking since the age of ten.
Wright was once a serial murderer and cannibal; who tortured, killed, butchered and ate seven human beings due to an "evil" hunger. As a result, he underwent neural resocialization to alter his memories and personality.
Wright became part of the crew of the Grey Tiger, which escorted a mercenary team (led by R. M. Dahl) secretly hired by "Mr. V." to protect archaeologists who were hired (also by "Mr. V") to unearth the Xel'Naga ruins found on the airless world of Nemaka. During the journey on board the battlecruiser Gray Tiger, he befriended archaeologist team leader Jake Ramsey.
Jake Ramsey was later possessed by a protoss mystic, who hatched a plot to free the then-imprisoned Ramsey. She reached into Wright's mind, who was guarding Ramsey at the time, and "undid" the resocialization. Wright suffered some mental agony, but regained his old memories as a murderous cannibal and wanted vengeance against the Dominion. Realizing that his friend Ramsey was somehow responsible for the discovery of his true self, he freed Ramsey and told him to "stay out of his way".
As Ramsey and Dahl escaped the Gray Tiger, Wright killed nine other marines and ate parts of them, then disabled the ship's life support. He left a brief message explaining his motives (which was later seen by Valerian Mengsk) and then shot himself while still on camera.
In the 2009 film, Terminator Salvation, another character named Marcus Wright has a similar premise. He is an inmate "reborn" through technology to serve. At the end Wright surmounts his programming and acts contrary to his intended purpose.