The Lurker was an early B.O.W. (Bio-Organic Weapon) which was developed by
James Marcus - it was created by injecting frogs with the
t-Virus Alpha strain. This early strain was known to increase the physical size and aggression of the infected. While research into amphibian-based B.O.W.s continued sporadically over time, Umbrella eventually decided that they were not a good fit and as such, further experiments were abandoned.
Through the infection affecting its body, the
t-Virus blinded the Lurker and increased its aggression to uncontrollable levels. However, as they were still closely related to their original form it was still possible to startle them and cause them to run and hide.
The creature itself was essentially an enlarged version of its standard form - but with its increased size came a vastly increased appetite also. Marcus' aim with the Lurker was to improve them to a state where their intelligence could be high enough that they could work or follow commands. As the end result did none of these things, all created prototypes were discarded.
The survivors wound up in a water treatment plant in the Arklay Mountains region.
Further research into amphibian B.O.W.s many years later included the Hunter Gamma (based on the frog, again) and the
Albinoid (based on the salamander) — and neither performed as expected.
