Jack Krauser is a formidable antagonist in the Biohazard (Resident Evil) series, first appearing in Resident Evil 4. Formerly a skilled operative and ally of Leon S. Kennedy, Krauser turns rogue and allies himself with the Los Illuminados cult. Known for his ruthless combat skills and genetically enhanced abilities, he presents a significant challenge to the protagonist. His motivations are driven by personal ambition and a desire for power, making him a memorable and complex villain within the series.