The Biologist
Although she is not the leader of the expedition team, the biologist is the protagonist of the book. She is never given a name—none of the characters are—but she is given a more extensive back-story than the others. We know that she keeps a detailed field journal, the final product of which makes up the text of the novel. We know that she joined the expedition at least partly because her husband had been on the previous trip. Her career in biology has been defined by her insatiable curiosity. When her husband returned home with huge gaps in his knowledge and confusion about himself, it led her to wonder what he came in contact with in Area X that could so fundamentally change him.
The biologist values courage and the pursuit of truth. She portrays herself as introverted and antisocial, but when it comes to the environments that she studies, she cannot remain objective. She implicates herself into the environment, even if she is forever relegated to the role of observer. As the novel progresses, her body undergoes changes due to the spores she inhaled when first investigating the tower. The changes immunize her from hypnosis and make her hyper-attuned to the environment of Area X.
The Psychologist
The leader of the expedition, the psychologist seems like somewhat of a villain of the piece because she has already planted trigger words in each of the team members. This suggests that she was trying to exert a surreptitious control over them. It also raises the question as to her motives. She sneaks off to the lighthouse herself, but something she encounters there chases her to her imminent death when she leaps from the top to save herself. She dies at the foot of the lighthouse.
The Anthropologist
The anthropologist is the least-developed character for the simple reason that she dies first. She disappears, and for a while it seems that the psychologist may have had something to do with this because she lies about her whereabouts and the circumstances of her disappearance. She is found at the bottom of the spiral staircase and is already dead when she is discovered.
The Surveyor
The Surveyor has a military background and takes the lead on strategic advancement. She is less trusting than the biologist and anthropologist are, but she also resists the idea of a mutiny against the psychologist because she is susceptible to hypnosis. The surveyor's military background is strongly emphasized throughout the novel as a major advantage of her presence on the expedition. When the biologist returns from her trip to the lighthouse, the surveyor ambushes her, but the biologist's heightened senses leave the surveyor outflanked and she is killed in the encounter.
The Biologist's Husband
The biologist's husband was a member of the eleventh expedition into Area X, the expedition immediately preceding the biologist's expedition. When he signed up for the expedition it caused an existing rift in their marriage to rapidly widen. The biologist's husband had a bold, outgoing personality. He loved socializing and relating to other people, had many friends from work, and was constantly concerned with how the biologist interacted, or failed to interact, with other people. He got into the habit of calling her "Ghost Bird," a half-affectionate, half-derisive nickname referring to the biologist's withdrawn manner. He suffered from a recurring nightmare from childhood through adolescence, but in college discovered that the contents of his nightmare were from an old horror movie he must've seen as an infant that imprinted on his memory.
The Lighthouse Keeper
Thirty years prior to the twelfth expedition, the lighthouse keeper mysteriously vanished. He appears to still be in Area X in some form, however, as the biologist is able to discern his face inside the writhing form of the Crawler.
