Robert is a 36-year-old former plant worker and military veteran stationed in Panama. As the seemingly last human man on Earth, he outfits his house into a fortress to protect himself from the Undead. He relies heavily on alcohol to cope with his profound isolation and the loss of his family, but eventually channels his energy into studying immunology and psychology to understand the vampiris bacteria.

Ruth is a young, slender, red-haired woman who appears in Los Angeles years after the initial outbreak. She claims to be a grieving survivor who recently lost her family to the disease. As Robert takes her into his home, her inconsistencies and physical aversions raise questions about her true motives.

Virginia is Robert's wife, who experiences the initial spread of the plague. She feels lethargic and suspects biological warfare is responsible for the strange weather and resistant mosquitoes. Her memory heavily influences Robert's current emotional state and his reluctance to leave his fortified home.

Kathy is the young daughter of Robert and Virginia. During the initial outbreak, she succumbs to the infection, forcing her father to comply with strict governmental regulations regarding the disposal of victims. Her former bedroom now serves as a storage space for Robert's nonperishable food.

Ben is Robert's former friend and carpool colleague at the local plant. Now infected and part of the Undead, he visits Robert's house nightly, persistently taunting him and trying to breach his defenses. He retains enough of his former personality to single out Robert specifically among the remaining population.

A stray dog that miraculously survives in the desolate streets of Los Angeles. Skittish and terrified, the dog initially hides from Robert's enthusiastic attempts to capture it. The animal becomes a vital target for Robert's need to nurture and connect with another living creature.