Abe is a widowed systems analyst at IBM in Poughkeepsie, New York. Following the tragic death of his young wife from cancer, he struggles with deep depression and alcohol dependency before discovering a meditative salvation in fishing. He is a mild-mannered, introverted man whose stoic personality contrasts with the strange events he encounters. His yearning for his late wife heavily influences his actions and worldview as he explores the Catskills' many streams.

Dan is an IBM employee and coworker of Abe who loses his wife and twin toddler sons when a truck strikes his car. He carries immense guilt over the accident and frequently visits the intersection where it occurred. Driven by an intense desperation to heal his shattered past, Dan begins to search for supernatural alternatives to ordinary grief, eventually fixating on a remote location known as Dutchman's Creek.

Rainer is a highly educated former professor of philology from Germany who works as a stonemason at the Ashokan Reservoir construction site. He possesses an extensive knowledge of languages and secret books that led to his exile from Europe. Despite his reputation as a rational skeptic, he recognizes the supernatural threat encroaching on his community and steps into a leadership position to protect his neighbors.

Lottie is a teenage German immigrant living in the Esopus Valley work camp during the early 20th century. She works in the camp's bakery alongside her mother, enjoying the lively atmosphere until strange occurrences shatter her peaceful routine. As the daughter of a former philology professor, she occasionally glimpses the dark texts her father hides, and her youthful innocence is heavily tested by the macabre events unfolding in her community.

Also known as the Guest, the Fisherman is a mysterious, seemingly immortal Hungarian sorcerer who takes up residence at the wealthy Dort estate. He possesses deep occult knowledge and pursues a centuries-long obsession with trapping a biblical beast known as the Leviathan. According to local lore, he seeks to harness unimaginable power to reverse a horrific family tragedy from his past, feeding upon the grief and secrets of ordinary people to maintain his strength.

Marie is Abe's beloved late wife who died of breast cancer shortly after their honeymoon. She was fifteen years younger than Abe and worked with him at IBM. Her memory heavily influences Abe's emotional state, and he often dreams of her in strange, aquatic contexts.

Sophie is Dan's deceased wife who died alongside their twin sons in a sudden traffic collision. Her sudden loss leaves an unfillable void in Dan's life, driving his obsessive actions and desire to seek out Dutchman's Creek.

Howard is the lantern-jawed proprietor of Herman's Café, a small diner located near the Ashokan Reservoir. He is a convivial and well-liked man who acts as the custodian of local folklore. Recognizing the danger of Dutchman's Creek, he feels an urgent responsibility to pass along a terrifying historical account to deter careless fishermen from visiting the area.

Clara is Rainer Schmidt's practical and fiercely protective wife. After fleeing Germany due to her husband's academic scandal, she finds solace working in the camp bakery with her daughter. She eventually demands that Rainer use his forbidden knowledge to defend their community when supernatural threats arise.

Helen is a Hungarian immigrant living in the Esopus Valley work camp. Following her accidental death, she seemingly returns from the grave, altered into a water-logged, golden-eyed entity. She uses her unholy state to expose the darkest secrets of the camp's residents, threatening the fragile peace of the community.

George is Helen's grieving husband, known for his infidelities while she was alive. Overcome by remorse following her sudden death, he makes a desperate pact with the man in the big house to secure a miraculous resurrection for his wife, unleashing a horrific chain of events.

Italo is an Italian stonemason living in the Ashokan camp who befriends Rainer Schmidt. He is a fiercely protective family man who quickly recognizes the demonic nature of his resurrected neighbor, Helen. He arms himself with an axe and joins Rainer's group to confront the source of the evil.

Jacob is a young Austrian immigrant working in the Esopus Valley who hopes to marry Lottie. Despite Rainer's initial bias against Austrians, Jacob proves his bravery by joining the dangerous expedition to Dort House. His courage during the supernatural confrontation earns him Rainer's lasting respect.

Cornelius is a wealthy, cantankerous tycoon in the 1840s Esopus Valley who owns the local estate known as the Station. He welcomes the mysterious Fisherman into his home and soon begins shipping bizarre, unnatural hides to local tanners.

Angelo is a worker in the Esopus Valley camp who joins Rainer Schmidt's expedition to the Dort House. He bravely wields an axe against the massive fishing lines holding the Leviathan but soon faces the terrifying reality of the Fisherman's dark magic.

Wilhelm is a former academic colleague of Rainer Schmidt. He shared Rainer's dangerous obsession with prehistoric, magical languages, leading to a catastrophic expedition beneath a German city that fundamentally altered the course of Rainer's life.

Reverend Mapple is a Lutheran minister based in Woodstock who accidentally triggers Lottie Schmidt's hidden memories. He solemnly promises to avoid Dutchman's Creek in exchange for hearing her terrifying historical account, which he later passes on to Howard.

The Leviathan is a colossal, primordial beast of biblical proportions that resides in a black ocean beneath the earth. It is described as vast, limbless, and colorless, possessing power closer to a god than a devil. The creature serves as the ultimate prize for the Fisherman's centuries-long hunt.

Beatrice is the much-younger wife of Cornelius Dort. She suffers a tragic miscarriage after falling from a horse and languishes in a near-death state, prompting local rumors about the true nature of her husband's mysterious Guest.

Gretchen is one of Lottie Schmidt's younger sisters. She lives with her family in the bustling work camp and relies on her parents to shield her from the terrifying supernatural occurrences that plague their neighborhood.

Christina is the youngest daughter of Rainer and Clara Schmidt. Like her sister Gretchen, she lives unaware of the true depths of the occult danger surrounding the camp, depending entirely on her family's protection.

Regina is Italo's wife, a kind-hearted woman who takes in her neighbors' children during a crisis. Her compassion places her directly in the path of the resurrected Helen, leading to a terrifying confrontation at her own front door.

Giovanni is the young son of Italo and Regina. He becomes a direct victim of the supernatural terror invading the camp when Helen reaches through a loose board in his home and physically assaults him.

Maria is the eldest child of George and Helen. Following her mother's tragic death and her father's erratic behavior, she attempts to care for her younger siblings, eventually stepping into a permanent nurturing role for her family.

Andrea is Angelo's brother and a fellow worker at the Ashokan camp. He accompanies Rainer to the Dort House to destroy the massive fishing lines holding the Leviathan, witnessing unimaginable horrors alongside his brother.