He was a Corporal serving in the Menlonian Ground Forces’ special forces unit. He was deployed to a laboratory during the WE-30 virus outbreak as part of the first wave of soldiers sent to contain the disaster. Even before the outbreak, Gilbert had a dangerous reputation. Evaluation teams considered him unstable and warned that he shouldn't be trusted with a gun. Despite these concerns, he was deployed as an armed pointman, carrying an R8 shotgun. During the mission, Gilbert served alongside a soldier known as Chimera, whose real name was Kayden Troy, as well as a Corpsman and an Operative. The mission ended in disaster: the Corpsman and Operative died, while Gilbert and Chimera became infected with WE-30. The infection transformed Gilbert into a terrifying enemy who retained his combat abilities and continued wielding his shotgun. He became a relentless killing machine, attacking both survivors and other infected. However, Gilbert appears to retain fragments of his former mind. He still calls out to Troy and other comrades, suggesting that some memories of his old life remain. His inability to fully control his infected body makes him a tragic character: a soldier who remembers pieces of his past but can no longer reliably distinguish friend from foe. His terrifying reputation, combined with his deadly shotgun and lingering memories, makes Gilbert one of the game's most memorable infected enemies.