Lurkers (ラーカー,rākā?) were a species of frog created in the early years of t-Virus research as part of a study in the effects of mutation on amphibians and their suitability as bio-weapons. Created by Dr. James Marcus, the failures in the Lurker indicated that amphibian-based bio-weapons were impractical with the t-Virus strains available at the time. The only other known prototype amphibian bio-weapon was the Hunter γ over fifteen years later, which suffered the same flaws. Mutants of a similar appearance to the Lurker were spotted in the sewers during the Raccoon City Destruction Incident.
In his research on Progenitor and the early t-Virus strains, Dr. James Marcus chose frogs to represent the Amphibia class of animal. The infected frogs were largely unbenefited by the viral infection, only increasing in size. It was largely agreed in Umbrella research for years to come that a bio-weapon should have both strength and intellect; as the Lurker's brainpower did not improve beyond that of the frog species it was based on, it was unsuitable for military sales. Without intelligence, the increased aggression associated with t-Virus infection would merely make it a danger to potential keepers.