Darkseekers are the antagonists of the 2007 film adaption, I Am Legend. They are the humans susceptible to the Krippin Virus who were infected, but did not die from it.
Info
While those infected with KV who survive it develop primal behaviour upon succumbing to the virus and becoming a Darkseeker, they do retain enough of their higher intelligence to build and copy complex traps they have previously seen. Darkseekers' adrenal glands are always open, giving the Darkseekers increased strength and mobility. However, it also speeds up their metabolism, resulting in cannibalism when food is scarce. The increased metabolism also speeds up Darkseekers' heart rate, breathing speed and body temperature, and makes them constantly hyperventilate.
Other symptoms of KV include dilated pupils, enflamed gums (in infected dogs at least), hair loss, albinism, and a primal state of rage. Another major symptom is a severe, vampire-like intolerance of UV radiation, causing sunlight and other sources of ultraviolet to burn Darkseekers (causing a similar effect to the volatiles and the night hunter in Dying Light). Because of this intolerance of UV, Darkseekers are forced into a nocturnal life cycle; lurking in dark, derelict buildings during the day, and only leaving at night. The intolerance of UV is also so extreme, direct exposure to sunlight for more than a matter of seconds can be fatal to a Darkseeker. Darkseekers are also attracted to and crave blood, much like the traditional vampire, and see the uninfected as vicious monsters that must be destroyed.
Abilities
Darkseekers scaling the walls of Neville's apartment
As their adrenal glands are constantly open, Darkseekers possess adrenaline-enhanced strength, speed and endurance. Darkseekers apparently also gain a heightned sense of smell, as Neville had to bleach the scent on his home's doorstep before sunset, and the female specimen was easily drawn by a sample of Neville's blood.
Darkseekers also retain enough of their higher levels of intelligence to set up elaborate traps they have previously seen, such as snare traps.