Jack Krauser is a freelance mercenary hired by Albert Wesker to infiltrate Saddler's cult.
Originally a U.S. government special forces operative, he was partnered with Leon Kennedy to arrest the South American drug lord Javier Hidalgo. They discover the village suffering a T-Virus outbreak while encountering Manuela Hidalgo who was injected with the T-Veronica Virus, Krauser learning of Wesker and the Umbrella conspiracy from Leon.
Discharged from the military after his arm severely injured from fighting Hidalgo, Krauser seeks out Wesker to recover from his injury and become stronger. He later supposedly perished in a helicopter crash. Krauser is responsible for kidnapping Ashley, claiming he committed the act to gain Saddler's trust. He has little interest in Saddler's agenda, and only seeks to recover Las Plagas sample for Wesker for the latter's plan to restore the then-defunct Umbrella Corporation, believing such would bring order and balance to the world. In addition to being a skilled knife fighter and archer, Krauser possesses superhuman speed, stamina, strength, the dominant variant of Las Plagas injected into his body can turn his left arm into a giant mutated claw.
He confronts Kennedy twice in the game's main storyline and is defeated by him, later killed by Ada Wong in the "Separate Ways" scenario. It would be later revealed that Wesker retrieve Krauser's corpse and extracted his Las Plagas after Ada gave him a recessive variant. Krauser is playable in Mercenaries mode. He uses his bow in combat and can also utilize his mutated arm as a melee weapon.